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b97efd5e98
Pull KCSAN updates from Paul McKenney. * 'kcsan.2021.05.18a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: kcsan: Use URL link for pointing access-marking.txt kcsan: Document "value changed" line kcsan: Report observed value changes kcsan: Remove kcsan_report_type kcsan: Remove reporting indirection kcsan: Refactor access_info initialization kcsan: Fold panic() call into print_report() kcsan: Refactor passing watchpoint/other_info kcsan: Distinguish kcsan_report() calls kcsan: Simplify value change detection kcsan: Add pointer to access-marking.txt to data_race() bullet
655 lines
19 KiB
C
655 lines
19 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* KCSAN reporting.
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*
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* Copyright (C) 2019, Google LLC.
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*/
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#include <linux/debug_locks.h>
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#include <linux/delay.h>
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#include <linux/jiffies.h>
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#include <linux/kernel.h>
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#include <linux/lockdep.h>
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#include <linux/preempt.h>
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#include <linux/printk.h>
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#include <linux/sched.h>
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#include <linux/spinlock.h>
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#include <linux/stacktrace.h>
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#include "kcsan.h"
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#include "encoding.h"
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/*
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* Max. number of stack entries to show in the report.
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*/
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#define NUM_STACK_ENTRIES 64
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/* Common access info. */
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struct access_info {
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const volatile void *ptr;
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size_t size;
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int access_type;
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int task_pid;
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int cpu_id;
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};
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/*
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* Other thread info: communicated from other racing thread to thread that set
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* up the watchpoint, which then prints the complete report atomically.
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*/
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struct other_info {
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struct access_info ai;
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unsigned long stack_entries[NUM_STACK_ENTRIES];
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int num_stack_entries;
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/*
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* Optionally pass @current. Typically we do not need to pass @current
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* via @other_info since just @task_pid is sufficient. Passing @current
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* has additional overhead.
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*
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* To safely pass @current, we must either use get_task_struct/
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* put_task_struct, or stall the thread that populated @other_info.
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*
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* We cannot rely on get_task_struct/put_task_struct in case
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* release_report() races with a task being released, and would have to
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* free it in release_report(). This may result in deadlock if we want
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* to use KCSAN on the allocators.
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*
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* Since we also want to reliably print held locks for
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* CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
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* that populated @other_info until it has been consumed.
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*/
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struct task_struct *task;
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};
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/*
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* To never block any producers of struct other_info, we need as many elements
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* as we have watchpoints (upper bound on concurrent races to report).
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*/
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static struct other_info other_infos[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
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/*
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* Information about reported races; used to rate limit reporting.
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*/
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struct report_time {
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/*
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* The last time the race was reported.
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*/
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unsigned long time;
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/*
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* The frames of the 2 threads; if only 1 thread is known, one frame
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* will be 0.
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*/
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unsigned long frame1;
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unsigned long frame2;
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};
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/*
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* Since we also want to be able to debug allocators with KCSAN, to avoid
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* deadlock, report_times cannot be dynamically resized with krealloc in
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* rate_limit_report.
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*
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* Therefore, we use a fixed-size array, which at most will occupy a page. This
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* still adequately rate limits reports, assuming that a) number of unique data
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* races is not excessive, and b) occurrence of unique races within the
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* same time window is limited.
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*/
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#define REPORT_TIMES_MAX (PAGE_SIZE / sizeof(struct report_time))
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#define REPORT_TIMES_SIZE \
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(CONFIG_KCSAN_REPORT_ONCE_IN_MS > REPORT_TIMES_MAX ? \
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REPORT_TIMES_MAX : \
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CONFIG_KCSAN_REPORT_ONCE_IN_MS)
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static struct report_time report_times[REPORT_TIMES_SIZE];
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/*
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* Spinlock serializing report generation, and access to @other_infos. Although
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* it could make sense to have a finer-grained locking story for @other_infos,
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* report generation needs to be serialized either way, so not much is gained.
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*/
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static DEFINE_RAW_SPINLOCK(report_lock);
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/*
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* Checks if the race identified by thread frames frame1 and frame2 has
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* been reported since (now - KCSAN_REPORT_ONCE_IN_MS).
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*/
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static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
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{
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struct report_time *use_entry = &report_times[0];
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unsigned long invalid_before;
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int i;
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BUILD_BUG_ON(CONFIG_KCSAN_REPORT_ONCE_IN_MS != 0 && REPORT_TIMES_SIZE == 0);
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if (CONFIG_KCSAN_REPORT_ONCE_IN_MS == 0)
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return false;
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invalid_before = jiffies - msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS);
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/* Check if a matching race report exists. */
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for (i = 0; i < REPORT_TIMES_SIZE; ++i) {
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struct report_time *rt = &report_times[i];
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/*
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* Must always select an entry for use to store info as we
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* cannot resize report_times; at the end of the scan, use_entry
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* will be the oldest entry, which ideally also happened before
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* KCSAN_REPORT_ONCE_IN_MS ago.
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*/
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if (time_before(rt->time, use_entry->time))
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use_entry = rt;
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/*
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* Initially, no need to check any further as this entry as well
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* as following entries have never been used.
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*/
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if (rt->time == 0)
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break;
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/* Check if entry expired. */
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if (time_before(rt->time, invalid_before))
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continue; /* before KCSAN_REPORT_ONCE_IN_MS ago */
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/* Reported recently, check if race matches. */
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if ((rt->frame1 == frame1 && rt->frame2 == frame2) ||
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(rt->frame1 == frame2 && rt->frame2 == frame1))
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return true;
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}
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use_entry->time = jiffies;
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use_entry->frame1 = frame1;
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use_entry->frame2 = frame2;
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return false;
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}
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/*
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* Special rules to skip reporting.
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*/
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static bool
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skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
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{
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/* Should never get here if value_change==FALSE. */
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WARN_ON_ONCE(value_change == KCSAN_VALUE_CHANGE_FALSE);
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/*
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* The first call to skip_report always has value_change==TRUE, since we
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* cannot know the value written of an instrumented access. For the 2nd
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* call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
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*
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* 1. read watchpoint, conflicting write (value_change==TRUE): report;
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* 2. read watchpoint, conflicting write (value_change==MAYBE): skip;
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* 3. write watchpoint, conflicting write (value_change==TRUE): report;
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* 4. write watchpoint, conflicting write (value_change==MAYBE): skip;
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* 5. write watchpoint, conflicting read (value_change==MAYBE): skip;
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* 6. write watchpoint, conflicting read (value_change==TRUE): report;
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*
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* Cases 1-4 are intuitive and expected; case 5 ensures we do not report
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* data races where the write may have rewritten the same value; case 6
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* is possible either if the size is larger than what we check value
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* changes for or the access type is KCSAN_ACCESS_ASSERT.
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*/
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if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) &&
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value_change == KCSAN_VALUE_CHANGE_MAYBE) {
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/*
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* The access is a write, but the data value did not change.
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*
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* We opt-out of this filter for certain functions at request of
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* maintainers.
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*/
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char buf[64];
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int len = scnprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
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if (!strnstr(buf, "rcu_", len) &&
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!strnstr(buf, "_rcu", len) &&
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!strnstr(buf, "_srcu", len))
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return true;
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}
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return kcsan_skip_report_debugfs(top_frame);
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}
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static const char *get_access_type(int type)
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{
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if (type & KCSAN_ACCESS_ASSERT) {
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if (type & KCSAN_ACCESS_SCOPED) {
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if (type & KCSAN_ACCESS_WRITE)
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return "assert no accesses (scoped)";
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else
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return "assert no writes (scoped)";
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} else {
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if (type & KCSAN_ACCESS_WRITE)
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return "assert no accesses";
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else
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return "assert no writes";
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}
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}
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switch (type) {
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case 0:
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return "read";
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case KCSAN_ACCESS_ATOMIC:
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return "read (marked)";
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case KCSAN_ACCESS_WRITE:
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return "write";
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case KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
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return "write (marked)";
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case KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE:
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return "read-write";
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case KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
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return "read-write (marked)";
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case KCSAN_ACCESS_SCOPED:
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return "read (scoped)";
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case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_ATOMIC:
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return "read (marked, scoped)";
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case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE:
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return "write (scoped)";
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case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC:
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return "write (marked, scoped)";
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default:
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BUG();
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}
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}
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static const char *get_bug_type(int type)
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{
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return (type & KCSAN_ACCESS_ASSERT) != 0 ? "assert: race" : "data-race";
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}
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/* Return thread description: in task or interrupt. */
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static const char *get_thread_desc(int task_id)
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{
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if (task_id != -1) {
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static char buf[32]; /* safe: protected by report_lock */
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snprintf(buf, sizeof(buf), "task %i", task_id);
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return buf;
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}
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return "interrupt";
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}
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/* Helper to skip KCSAN-related functions in stack-trace. */
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static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)
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{
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char buf[64];
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char *cur;
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int len, skip;
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for (skip = 0; skip < num_entries; ++skip) {
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len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
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/* Never show tsan_* or {read,write}_once_size. */
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if (strnstr(buf, "tsan_", len) ||
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strnstr(buf, "_once_size", len))
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continue;
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cur = strnstr(buf, "kcsan_", len);
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if (cur) {
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cur += strlen("kcsan_");
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if (!str_has_prefix(cur, "test"))
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continue; /* KCSAN runtime function. */
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/* KCSAN related test. */
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}
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/*
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* No match for runtime functions -- @skip entries to skip to
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* get to first frame of interest.
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*/
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break;
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}
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return skip;
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}
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/* Compares symbolized strings of addr1 and addr2. */
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static int sym_strcmp(void *addr1, void *addr2)
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{
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char buf1[64];
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char buf2[64];
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snprintf(buf1, sizeof(buf1), "%pS", addr1);
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snprintf(buf2, sizeof(buf2), "%pS", addr2);
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return strncmp(buf1, buf2, sizeof(buf1));
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}
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static void print_verbose_info(struct task_struct *task)
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{
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if (!task)
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return;
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/* Restore IRQ state trace for printing. */
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kcsan_restore_irqtrace(task);
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pr_err("\n");
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debug_show_held_locks(task);
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print_irqtrace_events(task);
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}
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static void print_report(enum kcsan_value_change value_change,
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const struct access_info *ai,
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const struct other_info *other_info,
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u64 old, u64 new, u64 mask)
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{
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unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
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int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
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int skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
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unsigned long this_frame = stack_entries[skipnr];
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unsigned long other_frame = 0;
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int other_skipnr = 0; /* silence uninit warnings */
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/*
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* Must check report filter rules before starting to print.
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*/
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if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
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return;
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if (other_info) {
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other_skipnr = get_stack_skipnr(other_info->stack_entries,
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other_info->num_stack_entries);
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other_frame = other_info->stack_entries[other_skipnr];
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/* @value_change is only known for the other thread */
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if (skip_report(value_change, other_frame))
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return;
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}
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if (rate_limit_report(this_frame, other_frame))
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return;
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/* Print report header. */
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pr_err("==================================================================\n");
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if (other_info) {
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int cmp;
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/*
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* Order functions lexographically for consistent bug titles.
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* Do not print offset of functions to keep title short.
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*/
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cmp = sym_strcmp((void *)other_frame, (void *)this_frame);
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pr_err("BUG: KCSAN: %s in %ps / %ps\n",
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get_bug_type(ai->access_type | other_info->ai.access_type),
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(void *)(cmp < 0 ? other_frame : this_frame),
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(void *)(cmp < 0 ? this_frame : other_frame));
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} else {
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pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(ai->access_type),
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(void *)this_frame);
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}
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pr_err("\n");
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/* Print information about the racing accesses. */
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if (other_info) {
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pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
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get_access_type(other_info->ai.access_type), other_info->ai.ptr,
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other_info->ai.size, get_thread_desc(other_info->ai.task_pid),
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other_info->ai.cpu_id);
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/* Print the other thread's stack trace. */
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stack_trace_print(other_info->stack_entries + other_skipnr,
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other_info->num_stack_entries - other_skipnr,
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0);
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if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
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print_verbose_info(other_info->task);
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pr_err("\n");
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pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
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get_access_type(ai->access_type), ai->ptr, ai->size,
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get_thread_desc(ai->task_pid), ai->cpu_id);
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} else {
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pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",
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get_access_type(ai->access_type), ai->ptr, ai->size,
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get_thread_desc(ai->task_pid), ai->cpu_id);
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}
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/* Print stack trace of this thread. */
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stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
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0);
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if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
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print_verbose_info(current);
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/* Print observed value change. */
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if (ai->size <= 8) {
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int hex_len = ai->size * 2;
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u64 diff = old ^ new;
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if (mask)
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diff &= mask;
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if (diff) {
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pr_err("\n");
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pr_err("value changed: 0x%0*llx -> 0x%0*llx\n",
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hex_len, old, hex_len, new);
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if (mask) {
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pr_err(" bits changed: 0x%0*llx with mask 0x%0*llx\n",
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hex_len, diff, hex_len, mask);
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}
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}
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}
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/* Print report footer. */
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pr_err("\n");
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pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
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dump_stack_print_info(KERN_DEFAULT);
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pr_err("==================================================================\n");
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if (panic_on_warn)
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panic("panic_on_warn set ...\n");
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}
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static void release_report(unsigned long *flags, struct other_info *other_info)
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{
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/*
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* Use size to denote valid/invalid, since KCSAN entirely ignores
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* 0-sized accesses.
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*/
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other_info->ai.size = 0;
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raw_spin_unlock_irqrestore(&report_lock, *flags);
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}
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/*
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* Sets @other_info->task and awaits consumption of @other_info.
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*
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* Precondition: report_lock is held.
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* Postcondition: report_lock is held.
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*/
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static void set_other_info_task_blocking(unsigned long *flags,
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const struct access_info *ai,
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struct other_info *other_info)
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{
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/*
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* We may be instrumenting a code-path where current->state is already
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* something other than TASK_RUNNING.
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*/
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const bool is_running = task_is_running(current);
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/*
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* To avoid deadlock in case we are in an interrupt here and this is a
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* race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
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* timeout to ensure this works in all contexts.
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*
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* Await approximately the worst case delay of the reporting thread (if
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* we are not interrupted).
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*/
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int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
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other_info->task = current;
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do {
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if (is_running) {
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/*
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* Let lockdep know the real task is sleeping, to print
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* the held locks (recall we turned lockdep off, so
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* locking/unlocking @report_lock won't be recorded).
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*/
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set_current_state(TASK_UNINTERRUPTIBLE);
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}
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raw_spin_unlock_irqrestore(&report_lock, *flags);
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/*
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* We cannot call schedule() since we also cannot reliably
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* determine if sleeping here is permitted -- see in_atomic().
|
|
*/
|
|
|
|
udelay(1);
|
|
raw_spin_lock_irqsave(&report_lock, *flags);
|
|
if (timeout-- < 0) {
|
|
/*
|
|
* Abort. Reset @other_info->task to NULL, since it
|
|
* appears the other thread is still going to consume
|
|
* it. It will result in no verbose info printed for
|
|
* this task.
|
|
*/
|
|
other_info->task = NULL;
|
|
break;
|
|
}
|
|
/*
|
|
* If invalid, or @ptr nor @current matches, then @other_info
|
|
* has been consumed and we may continue. If not, retry.
|
|
*/
|
|
} while (other_info->ai.size && other_info->ai.ptr == ai->ptr &&
|
|
other_info->task == current);
|
|
if (is_running)
|
|
set_current_state(TASK_RUNNING);
|
|
}
|
|
|
|
/* Populate @other_info; requires that the provided @other_info not in use. */
|
|
static void prepare_report_producer(unsigned long *flags,
|
|
const struct access_info *ai,
|
|
struct other_info *other_info)
|
|
{
|
|
raw_spin_lock_irqsave(&report_lock, *flags);
|
|
|
|
/*
|
|
* The same @other_infos entry cannot be used concurrently, because
|
|
* there is a one-to-one mapping to watchpoint slots (@watchpoints in
|
|
* core.c), and a watchpoint is only released for reuse after reporting
|
|
* is done by the consumer of @other_info. Therefore, it is impossible
|
|
* for another concurrent prepare_report_producer() to set the same
|
|
* @other_info, and are guaranteed exclusivity for the @other_infos
|
|
* entry pointed to by @other_info.
|
|
*
|
|
* To check this property holds, size should never be non-zero here,
|
|
* because every consumer of struct other_info resets size to 0 in
|
|
* release_report().
|
|
*/
|
|
WARN_ON(other_info->ai.size);
|
|
|
|
other_info->ai = *ai;
|
|
other_info->num_stack_entries = stack_trace_save(other_info->stack_entries, NUM_STACK_ENTRIES, 2);
|
|
|
|
if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
|
|
set_other_info_task_blocking(flags, ai, other_info);
|
|
|
|
raw_spin_unlock_irqrestore(&report_lock, *flags);
|
|
}
|
|
|
|
/* Awaits producer to fill @other_info and then returns. */
|
|
static bool prepare_report_consumer(unsigned long *flags,
|
|
const struct access_info *ai,
|
|
struct other_info *other_info)
|
|
{
|
|
|
|
raw_spin_lock_irqsave(&report_lock, *flags);
|
|
while (!other_info->ai.size) { /* Await valid @other_info. */
|
|
raw_spin_unlock_irqrestore(&report_lock, *flags);
|
|
cpu_relax();
|
|
raw_spin_lock_irqsave(&report_lock, *flags);
|
|
}
|
|
|
|
/* Should always have a matching access based on watchpoint encoding. */
|
|
if (WARN_ON(!matching_access((unsigned long)other_info->ai.ptr & WATCHPOINT_ADDR_MASK, other_info->ai.size,
|
|
(unsigned long)ai->ptr & WATCHPOINT_ADDR_MASK, ai->size)))
|
|
goto discard;
|
|
|
|
if (!matching_access((unsigned long)other_info->ai.ptr, other_info->ai.size,
|
|
(unsigned long)ai->ptr, ai->size)) {
|
|
/*
|
|
* If the actual accesses to not match, this was a false
|
|
* positive due to watchpoint encoding.
|
|
*/
|
|
atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ENCODING_FALSE_POSITIVES]);
|
|
goto discard;
|
|
}
|
|
|
|
return true;
|
|
|
|
discard:
|
|
release_report(flags, other_info);
|
|
return false;
|
|
}
|
|
|
|
static struct access_info prepare_access_info(const volatile void *ptr, size_t size,
|
|
int access_type)
|
|
{
|
|
return (struct access_info) {
|
|
.ptr = ptr,
|
|
.size = size,
|
|
.access_type = access_type,
|
|
.task_pid = in_task() ? task_pid_nr(current) : -1,
|
|
.cpu_id = raw_smp_processor_id()
|
|
};
|
|
}
|
|
|
|
void kcsan_report_set_info(const volatile void *ptr, size_t size, int access_type,
|
|
int watchpoint_idx)
|
|
{
|
|
const struct access_info ai = prepare_access_info(ptr, size, access_type);
|
|
unsigned long flags;
|
|
|
|
kcsan_disable_current();
|
|
lockdep_off(); /* See kcsan_report_known_origin(). */
|
|
|
|
prepare_report_producer(&flags, &ai, &other_infos[watchpoint_idx]);
|
|
|
|
lockdep_on();
|
|
kcsan_enable_current();
|
|
}
|
|
|
|
void kcsan_report_known_origin(const volatile void *ptr, size_t size, int access_type,
|
|
enum kcsan_value_change value_change, int watchpoint_idx,
|
|
u64 old, u64 new, u64 mask)
|
|
{
|
|
const struct access_info ai = prepare_access_info(ptr, size, access_type);
|
|
struct other_info *other_info = &other_infos[watchpoint_idx];
|
|
unsigned long flags = 0;
|
|
|
|
kcsan_disable_current();
|
|
/*
|
|
* Because we may generate reports when we're in scheduler code, the use
|
|
* of printk() could deadlock. Until such time that all printing code
|
|
* called in print_report() is scheduler-safe, accept the risk, and just
|
|
* get our message out. As such, also disable lockdep to hide the
|
|
* warning, and avoid disabling lockdep for the rest of the kernel.
|
|
*/
|
|
lockdep_off();
|
|
|
|
if (!prepare_report_consumer(&flags, &ai, other_info))
|
|
goto out;
|
|
/*
|
|
* Never report if value_change is FALSE, only when it is
|
|
* either TRUE or MAYBE. In case of MAYBE, further filtering may
|
|
* be done once we know the full stack trace in print_report().
|
|
*/
|
|
if (value_change != KCSAN_VALUE_CHANGE_FALSE)
|
|
print_report(value_change, &ai, other_info, old, new, mask);
|
|
|
|
release_report(&flags, other_info);
|
|
out:
|
|
lockdep_on();
|
|
kcsan_enable_current();
|
|
}
|
|
|
|
void kcsan_report_unknown_origin(const volatile void *ptr, size_t size, int access_type,
|
|
u64 old, u64 new, u64 mask)
|
|
{
|
|
const struct access_info ai = prepare_access_info(ptr, size, access_type);
|
|
unsigned long flags;
|
|
|
|
kcsan_disable_current();
|
|
lockdep_off(); /* See kcsan_report_known_origin(). */
|
|
|
|
raw_spin_lock_irqsave(&report_lock, flags);
|
|
print_report(KCSAN_VALUE_CHANGE_TRUE, &ai, NULL, old, new, mask);
|
|
raw_spin_unlock_irqrestore(&report_lock, flags);
|
|
|
|
lockdep_on();
|
|
kcsan_enable_current();
|
|
}
|