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Merge branch 'ras-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull RAS fix from Ingo Molnar:
 "Fix an RCU warning that triggers when /dev/mcelog is used"

* 'ras-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/mcelog: Get rid of RCU remnants
This commit is contained in:
Linus Torvalds 2017-11-05 12:12:51 -08:00
commit b21172cf6d
1 changed files with 25 additions and 92 deletions
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117
arch/x86/kernel/cpu/mcheck/dev-mcelog.c
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@ -24,14 +24,6 @@ static DEFINE_MUTEX(mce_chrdev_read_mutex);
static char mce_helper[128];
static char *mce_helper_argv[2] = { mce_helper, NULL };
#define mce_log_get_idx_check(p) \
({ \
RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() && \
!lockdep_is_held(&mce_chrdev_read_mutex), \
"suspicious mce_log_get_idx_check() usage"); \
smp_load_acquire(&(p)); \
})
/*
* Lockless MCE logging infrastructure.
* This avoids deadlocks on printk locks without having to break locks. Also
@ -53,43 +45,32 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
void *data)
{
struct mce *mce = (struct mce *)data;
unsigned int next, entry;
unsigned int entry;
wmb();
for (;;) {
entry = mce_log_get_idx_check(mcelog.next);
for (;;) {
mutex_lock(&mce_chrdev_read_mutex);
/*
* When the buffer fills up discard new entries.
* Assume that the earlier errors are the more
* interesting ones:
*/
if (entry >= MCE_LOG_LEN) {
set_bit(MCE_OVERFLOW,
(unsigned long *)&mcelog.flags);
return NOTIFY_OK;
}
/* Old left over entry. Skip: */
if (mcelog.entry[entry].finished) {
entry++;
continue;
}
break;
}
smp_rmb();
next = entry + 1;
if (cmpxchg(&mcelog.next, entry, next) == entry)
break;
entry = mcelog.next;
/*
* When the buffer fills up discard new entries. Assume that the
* earlier errors are the more interesting ones:
*/
if (entry >= MCE_LOG_LEN) {
set_bit(MCE_OVERFLOW, (unsigned long *)&mcelog.flags);
goto unlock;
}
mcelog.next = entry + 1;
memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
wmb();
mcelog.entry[entry].finished = 1;
wmb();
/* wake processes polling /dev/mcelog */
wake_up_interruptible(&mce_chrdev_wait);
unlock:
mutex_unlock(&mce_chrdev_read_mutex);
return NOTIFY_OK;
}
@ -177,13 +158,6 @@ static int mce_chrdev_release(struct inode *inode, struct file *file)
return 0;
}
static void collect_tscs(void *data)
{
unsigned long *cpu_tsc = (unsigned long *)data;
cpu_tsc[smp_processor_id()] = rdtsc();
}
static int mce_apei_read_done;
/* Collect MCE record of previous boot in persistent storage via APEI ERST. */
@ -231,14 +205,9 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
size_t usize, loff_t *off)
{
char __user *buf = ubuf;
unsigned long *cpu_tsc;
unsigned prev, next;
unsigned next;
int i, err;
cpu_tsc = kmalloc(nr_cpu_ids * sizeof(long), GFP_KERNEL);
if (!cpu_tsc)
return -ENOMEM;
mutex_lock(&mce_chrdev_read_mutex);
if (!mce_apei_read_done) {
@ -247,65 +216,29 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
goto out;
}
next = mce_log_get_idx_check(mcelog.next);
/* Only supports full reads right now */
err = -EINVAL;
if (*off != 0 || usize < MCE_LOG_LEN*sizeof(struct mce))
goto out;
next = mcelog.next;
err = 0;
prev = 0;
do {
for (i = prev; i < next; i++) {
unsigned long start = jiffies;
struct mce *m = &mcelog.entry[i];
while (!m->finished) {
if (time_after_eq(jiffies, start + 2)) {
memset(m, 0, sizeof(*m));
goto timeout;
}
cpu_relax();
}
smp_rmb();
err |= copy_to_user(buf, m, sizeof(*m));
buf += sizeof(*m);
timeout:
;
}
memset(mcelog.entry + prev, 0,
(next - prev) * sizeof(struct mce));
prev = next;
next = cmpxchg(&mcelog.next, prev, 0);
} while (next != prev);
synchronize_sched();
/*
* Collect entries that were still getting written before the
* synchronize.
*/
on_each_cpu(collect_tscs, cpu_tsc, 1);
for (i = next; i < MCE_LOG_LEN; i++) {
for (i = 0; i < next; i++) {
struct mce *m = &mcelog.entry[i];
if (m->finished && m->tsc < cpu_tsc[m->cpu]) {
err |= copy_to_user(buf, m, sizeof(*m));
smp_rmb();
buf += sizeof(*m);
memset(m, 0, sizeof(*m));
}
err |= copy_to_user(buf, m, sizeof(*m));
buf += sizeof(*m);
}
memset(mcelog.entry, 0, next * sizeof(struct mce));
mcelog.next = 0;
if (err)
err = -EFAULT;
out:
mutex_unlock(&mce_chrdev_read_mutex);
kfree(cpu_tsc);
return err ? err : buf - ubuf;
}