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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Subject: [BUG] mm: backing-dev: a possible sleep-in-atomic-context bug in
 cgwb_create()
Cc:     linux-mm@kvack.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Message-ID: <626acba3-c565-7e05-6c8b-0d100ff645c5@gmail.com>
Date:   Thu, 21 Jun 2018 11:02:58 +0800
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The kernel may sleep with holding a spinlock.
The function call path (from bottom to top) in Linux-4.16.7 is:

[FUNC] schedule
lib/percpu-refcount.c, 222:
         schedule in __percpu_ref_switch_mode
lib/percpu-refcount.c, 339:
         __percpu_ref_switch_mode in percpu_ref_kill_and_confirm
./include/linux/percpu-refcount.h, 127:
         percpu_ref_kill_and_confirm in percpu_ref_kill
mm/backing-dev.c, 545:
         percpu_ref_kill in cgwb_kill
mm/backing-dev.c, 576:
         cgwb_kill in cgwb_create
mm/backing-dev.c, 573:
         _raw_spin_lock_irqsave in cgwb_create

This bug is found by my static analysis tool (DSAC-2) and checked by my
code review.

I do not know how to correctly fix this bug, so I just report them.
Maybe cgwb_kill() should not be called with holding a spinlock.


Best wishes,
Jia-Ju Bai