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CSD-lock diagnostic updates for v6.13

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This commit switches from sched_clock() to ktime_get_mono_fast_ns(), which
 on x86 switches from the rdtsc instruction to the rdtscp instruction,
 thus avoiding instruction reorderings that cause false-positive reports
 of CSD-lock stalls of almost 2^46 nanoseconds.  These false positives
 are rare, but really are seen in the wild.
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Merge tag 'csd-lock.2024.11.16a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull CSD-lock update from Paul McKenney:
 "This switches from sched_clock() to ktime_get_mono_fast_ns(), which on
  x86 switches from the rdtsc instruction to the rdtscp instruction,
  thus avoiding instruction reorderings that cause false-positive
  reports of CSD-lock stalls of almost 2^46 nanoseconds. These false
  positives are rare, but really are seen in the wild"

* tag 'csd-lock.2024.11.16a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  locking/csd-lock: Switch from sched_clock() to ktime_get_mono_fast_ns()
This commit is contained in:
Linus Torvalds 2024-11-19 10:18:45 -08:00
commit 311e062ad5
1 changed files with 2 additions and 2 deletions
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4
kernel/smp.c
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@ -246,7 +246,7 @@ static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, in
return true; return true;
} }
ts2 = sched_clock(); ts2 = ktime_get_mono_fast_ns();
/* How long since we last checked for a stuck CSD lock.*/ /* How long since we last checked for a stuck CSD lock.*/
ts_delta = ts2 - *ts1; ts_delta = ts2 - *ts1;
if (likely(ts_delta <= csd_lock_timeout_ns * (*nmessages + 1) * if (likely(ts_delta <= csd_lock_timeout_ns * (*nmessages + 1) *
@ -321,7 +321,7 @@ static void __csd_lock_wait(call_single_data_t *csd)
int bug_id = 0; int bug_id = 0;
u64 ts0, ts1; u64 ts0, ts1;
ts1 = ts0 = sched_clock(); ts1 = ts0 = ktime_get_mono_fast_ns();
for (;;) { for (;;) {
if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id, &nmessages)) if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id, &nmessages))
break; break;