The patch titled
Subject: lib/nmi_backtrace,c: use printk_safe_flush_on_panic when triggering backtraces
has been added to the -mm tree. Its filename is
nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces.patch
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------------------------------------------------------
From: Hoeun Ryu <hoeun.ryu@xxxxxxx>
Subject: lib/nmi_backtrace,c: use printk_safe_flush_on_panic when triggering backtraces
Use printk_safe_flush_on_panic() in nmi_trigger_cpumask_backtrace().
nmi_trigger_cpumask_backtrace() can be called in NMI context. For example
the function is called in watchdog_overflow_callback() if the flag of
hardlockup backtrace (sysctl_hardlockup_all_cpu_backtrace) is true and
watchdog_overflow_callback() function is called in NMI context on some
architectures.
printk_safe_flush() eventually tries to lock logbuf_lock in vprintk_emit()
but the logbuf_lock can be already locked in preempted contexts (task or
irq in this case) or by other CPUs and it may cause deadlocks.
By using printk_safe_flush_on_panic() instead of printk_safe_flush() in in
nmi_trigger_cpumask_backtrace(), the backtrace triggering CPU can access
the lock safely as the lock is reinitialized before calling
printk_safe_flush(). The messages in logbuf can be corrupted if the NMI
context preempts other contexts or ignores the lock held by other CPUs
writing the buffer.
Link: http://lkml.kernel.org/r/1527232247-31693-1-git-send-email-hoeun.ryu@xxxxxxxxxxx
Signed-off-by: Hoeun Ryu <hoeun.ryu@xxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Philippe Ombredanne <pombredanne@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Liu, Changcheng" <changcheng.liu@xxxxxxxxx>
Cc: Hoeun Ryu <hoeun.ryu@xxxxxxx>
Cc: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/nmi_backtrace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN lib/nmi_backtrace.c~nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces lib/nmi_backtrace.c
--- a/lib/nmi_backtrace.c~nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces
+++ a/lib/nmi_backtrace.c
@@ -78,8 +78,11 @@ void nmi_trigger_cpumask_backtrace(const
/*
* Force flush any remote buffers that might be stuck in IRQ context
* and therefore could not run their irq_work.
+ * Call nmi-safe version of printk_safe_flush() because this function can be
+ * called in NMI context like watchdog_overflow_callback() if
+ * sysctl_hardlockup_all_cpu_backtrace is true.
*/
- printk_safe_flush();
+ printk_safe_flush_on_panic();
clear_bit_unlock(0, &backtrace_flag);
put_cpu();
_
Patches currently in -mm which might be from hoeun.ryu@xxxxxxx are
nmi_backtrace-use-printk_safe_flush_on_panic-when-triggering-backtraces.patch
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