Re: [PATCH] mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock

Sergey Senozhatsky
2023-04-04T02:11:48Z

On (23/04/04 09:37), Tetsuo Handa wrote:
> syzbot is reporting circular locking dependency which involves
> zonelist_update_seq seqlock [1], for this lock is checked by memory
> allocation requests which do not need to be retried.
>
> We somehow need to prevent __alloc_pages_slowpath() from checking
> this lock. Since Petr Mladek thinks that __build_all_zonelists() can
> become a candidate for deferring printk() [2], let's make sure that
> current CPU/thread won't reach __alloc_pages_slowpath() while this lock
> is in use.
>
> Reported-by: syzbot <syzbot+223c7461c58c58a4cb10@syzkaller.appspotmail.com>
> Link: https://syzkaller.appspot.com/bug?extid=223c7461c58c58a4cb10 [1]
> Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation")
> Link: https://lkml.kernel.org/r/ZCrs+1cDqPWTDFNM@alley [2]
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Petr Mladek <pmladek@suse.com>

Yeah that looks like one of those printk_deferred() cases.
FWIW
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>