lkml.org 
[lkml]   [2020]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH printk 4/5] printk: remove logbuf_lock, add syslog_lock
Date
On 2020-09-24, Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:
> [..]
>> void printk_safe_flush_on_panic(void)
>> {
>> - /*
>> - * Make sure that we could access the main ring buffer.
>> - * Do not risk a double release when more CPUs are up.
>> - */
>> - if (raw_spin_is_locked(&logbuf_lock)) {
>> - if (num_online_cpus() > 1)
>> - return;
>> -
>> - debug_locks_off();
>> - raw_spin_lock_init(&logbuf_lock);
>
> If we panic() with syslog_lock locked then we need to zap syslog_lock
> and disable debug_locks for kmsg_dump() to succeed. Otherwise panic()
> may deadlock:
>
> syslog_lock_irq()
> -> NMI
> panic()
> ...
> printk_safe_flush_on_panic();
> kmsg_dump(KMSG_DUMP_PANIC); // syslog_lock_irqsave(flags)
> ...
>
> Did I miss the point where we make sure that kmsg_dump() will not
> deadlock?

You are correct. Thanks.

@clear_seq should either become atomic64 or kmsg_dump() should start
from the oldest available message (seq=0).

John Ogness

\
 
 \ /
  Last update: 2020-09-24 11:22    [W:0.103 / U:4.504 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site