The patch titled
Subject: softlockup: make detector be aware of task switch of processes hogging cpu
has been added to the -mm tree. Its filename is
softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: chai wen <chaiw.fnst@xxxxxxxxxxxxxx>
Subject: softlockup: make detector be aware of task switch of processes hogging cpu
For now, soft lockup detector warns once for each case of process
softlockup. But the thread 'watchdog/n' may not always get the cpu at the
time slot between the task switch of two processes hogging that cpu to
reset soft_watchdog_warn.
An example would be two processes hogging the cpu. Process A causes the
softlockup warning and is killed manually by a user. Process B
immediately becomes the new process hogging the cpu preventing the
softlockup code from resetting the soft_watchdog_warn variable.
This case is a false negative of "warn only once for a process", as there
may be a different process that is going to hog the cpu. Resolve this by
saving/checking the pid of the hogging process and use that to reset
soft_watchdog_warn too.
[dzickus@xxxxxxxxxx: modified the comment and changelog to be more specific]
Signed-off-by: chai wen <chaiw.fnst@xxxxxxxxxxxxxx>
Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff -puN kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu kernel/watchdog.c
--- a/kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu
+++ a/kernel/watchdog.c
@@ -42,6 +42,7 @@ static DEFINE_PER_CPU(bool, softlockup_t
static DEFINE_PER_CPU(bool, soft_watchdog_warn);
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
+static DEFINE_PER_CPU(pid_t, softlockup_warn_pid_saved);
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
@@ -319,6 +320,8 @@ static enum hrtimer_restart watchdog_tim
*/
duration = is_softlockup(touch_ts);
if (unlikely(duration)) {
+ pid_t pid = task_pid_nr(current);
+
/*
* If a virtual machine is stopped by the host it can look to
* the watchdog like a soft lockup, check to see if the host
@@ -328,8 +331,20 @@ static enum hrtimer_restart watchdog_tim
return HRTIMER_RESTART;
/* only warn once */
- if (__this_cpu_read(soft_watchdog_warn) == true)
+ if (__this_cpu_read(soft_watchdog_warn) == true) {
+
+ /*
+ * Handle the case where multiple processes are
+ * causing softlockups but the duration is small
+ * enough, the softlockup detector can not reset
+ * itself in time. Use pids to detect this.
+ */
+ if (__this_cpu_read(softlockup_warn_pid_saved) != pid) {
+ __this_cpu_write(soft_watchdog_warn, false);
+ __touch_watchdog();
+ }
return HRTIMER_RESTART;
+ }
if (softlockup_all_cpu_backtrace) {
/* Prevent multiple soft-lockup reports if one cpu is already
@@ -344,7 +359,8 @@ static enum hrtimer_restart watchdog_tim
pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
smp_processor_id(), duration,
- current->comm, task_pid_nr(current));
+ current->comm, pid);
+ __this_cpu_write(softlockup_warn_pid_saved, pid);
print_modules();
print_irqtrace_events(current);
if (regs)
_
Patches currently in -mm which might be from chaiw.fnst@xxxxxxxxxxxxxx are
watchdog-remove-unnecessary-head-files.patch
softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
