Messages in this thread | | | Date | Wed, 20 Jun 2018 20:35:15 -0700 | From | Matthew Wilcox <> | Subject | Re: [BUG] mm: backing-dev: a possible sleep-in-atomic-context bug in cgwb_create() |
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On Thu, Jun 21, 2018 at 11:02:58AM +0800, Jia-Ju Bai wrote: > 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 disagree with your code review.
* If the previous ATOMIC switching hasn't finished yet, wait for * its completion. If the caller ensures that ATOMIC switching * isn't in progress, this function can be called from any context.
I believe cgwb_kill is always called under the spinlock, so we will never sleep because the percpu ref will never be switching to atomic mode.
This is complex and subtle, so I could be wrong.
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