Merge branch 'ras-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
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
diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
index 10cec43..7f85b76 100644
--- a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
+++ b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
@@ -24,14 +24,6 @@
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 @@
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 @@
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 @@
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 @@
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;
}
