lkml.org 
[lkml]   [2020]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 1/1] powerpc/crash: Use NMI context for printk when starting to crash
Date
Currently, if printk lock (logbuf_lock) is held by other thread during
crash, there is a chance of deadlocking the crash on next printk, and
blocking a possibly desired kdump.

At the start of default_machine_crash_shutdown, make printk enter
NMI context, as it will use per-cpu buffers to store the message,
and avoid locking logbuf_lock.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>

---
Changes since v1:
- Added in-code comment explaining the need of context change
- Function moved to the start of default_machine_crash_shutdown,
to avoid locking any printk on crashing routine.
- Title was 'Use NMI context for printk after crashing other CPUs'

---
arch/powerpc/kexec/crash.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
index d488311efab1..c9a889880214 100644
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -311,6 +311,9 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
unsigned int i;
int (*old_handler)(struct pt_regs *regs);

+ /* Avoid hardlocking with irresponsive CPU holding logbuf_lock */
+ printk_nmi_enter();
+
/*
* This function is only called after the system
* has panicked or is otherwise in a critical state.
--
2.25.4
\
 
 \ /
  Last update: 2020-05-12 23:48    [W:0.059 / U:0.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site