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perf: Fix unclone_ctx() vs. locking

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The idiot who did 4a1c0f262f ("perf: Fix lockdep warning on process exit")
forgot to pay attention and fix all similar cases. Do so now.

In particular, unclone_ctx() must be called while holding ctx->lock,
therefore all such sites are broken for the same reason. Pull the
put_ctx() call out from under ctx->lock.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Probably-also-reported-by: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 4a1c0f262f ("perf: Fix lockdep warning on process exit")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Cong Wang <cwang@twopensource.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140930172308.GI4241@worktop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2014-09-30 19:23:08 +02:00 committed by Ingo Molnar
parent fe82dcec64
commit 211de6eba8
1 changed files with 31 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

54
kernel/events/core.c
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@ -902,13 +902,23 @@ static void put_ctx(struct perf_event_context *ctx)
}
}
static void unclone_ctx(struct perf_event_context *ctx)
/*
* This must be done under the ctx->lock, such as to serialize against
* context_equiv(), therefore we cannot call put_ctx() since that might end up
* calling scheduler related locks and ctx->lock nests inside those.
*/
static __must_check struct perf_event_context *
unclone_ctx(struct perf_event_context *ctx)
{
if (ctx->parent_ctx) {
put_ctx(ctx->parent_ctx);
struct perf_event_context *parent_ctx = ctx->parent_ctx;
lockdep_assert_held(&ctx->lock);
if (parent_ctx)
ctx->parent_ctx = NULL;
}
ctx->generation++;
return parent_ctx;
}
static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
@ -2210,6 +2220,9 @@ static void ctx_sched_out(struct perf_event_context *ctx,
static int context_equiv(struct perf_event_context *ctx1,
struct perf_event_context *ctx2)
{
lockdep_assert_held(&ctx1->lock);
lockdep_assert_held(&ctx2->lock);
/* Pinning disables the swap optimization */
if (ctx1->pin_count || ctx2->pin_count)
return 0;
@ -2943,6 +2956,7 @@ static int event_enable_on_exec(struct perf_event *event,
*/
static void perf_event_enable_on_exec(struct perf_event_context *ctx)
{
struct perf_event_context *clone_ctx = NULL;
struct perf_event *event;
unsigned long flags;
int enabled = 0;
@ -2974,7 +2988,7 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
* Unclone this context if we enabled any event.
*/
if (enabled)
unclone_ctx(ctx);
clone_ctx = unclone_ctx(ctx);
raw_spin_unlock(&ctx->lock);
@ -2984,6 +2998,9 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
perf_event_context_sched_in(ctx, ctx->task);
out:
local_irq_restore(flags);
if (clone_ctx)
put_ctx(clone_ctx);
}
void perf_event_exec(void)
@ -3135,7 +3152,7 @@ errout:
static struct perf_event_context *
find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
{
struct perf_event_context *ctx;
struct perf_event_context *ctx, *clone_ctx = NULL;
struct perf_cpu_context *cpuctx;
unsigned long flags;
int ctxn, err;
@ -3169,9 +3186,12 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
retry:
ctx = perf_lock_task_context(task, ctxn, &flags);
if (ctx) {
unclone_ctx(ctx);
clone_ctx = unclone_ctx(ctx);
++ctx->pin_count;
raw_spin_unlock_irqrestore(&ctx->lock, flags);
if (clone_ctx)
put_ctx(clone_ctx);
} else {
ctx = alloc_perf_context(pmu, task);
err = -ENOMEM;
@ -7523,7 +7543,7 @@ __perf_event_exit_task(struct perf_event *child_event,
static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
{
struct perf_event *child_event, *next;
struct perf_event_context *child_ctx, *parent_ctx;
struct perf_event_context *child_ctx, *clone_ctx = NULL;
unsigned long flags;
if (likely(!child->perf_event_ctxp[ctxn])) {
@ -7549,29 +7569,17 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
task_ctx_sched_out(child_ctx);
child->perf_event_ctxp[ctxn] = NULL;
/*
* In order to avoid freeing: child_ctx->parent_ctx->task
* under perf_event_context::lock, grab another reference.
*/
parent_ctx = child_ctx->parent_ctx;
if (parent_ctx)
get_ctx(parent_ctx);
/*
* If this context is a clone; unclone it so it can't get
* swapped to another process while we're removing all
* the events from it.
*/
unclone_ctx(child_ctx);
clone_ctx = unclone_ctx(child_ctx);
update_context_time(child_ctx);
raw_spin_unlock_irqrestore(&child_ctx->lock, flags);
/*
* Now that we no longer hold perf_event_context::lock, drop
* our extra child_ctx->parent_ctx reference.
*/
if (parent_ctx)
put_ctx(parent_ctx);
if (clone_ctx)
put_ctx(clone_ctx);
/*
* Report the task dead after unscheduling the events so that we