Messages in this thread | | | From | Petr Mladek <> | Subject | [PATCH 0/3] kthread_worker: Fix race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() | Date | Thu, 10 Jun 2021 15:30:48 +0200 |
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This patchset fixes the race between kthread_mod_delayed_work() and kthread_cancel_delayed_work_sync() including proper return value handling.
The original fix, from Martin Liu [1], opened discussion [2] about the return value. It took me some time to realize that the original patch was not a correct fix.
The problem is that the return value might be used for reference counting of the queued works. The return value is boolean. It could distinguish only two situations where the work is:
+ newly queued => inc(refcnt) (ret == false) + was queued, removed, added => nope(refcntn) (ret == true)
The original fix, introduced another situation:
+ was queued, removed => dec(refcnt) (ret == ???)
The proper solution is to remove the work from the list only when it can be added again. Fortunately, it can be fixed relatively easily. I have split it into 3 small steps.
[1] https://lore.kernel.org/r/20210513065458.941403-1-liumartin@google.com [2] https://lore.kernel.org/r/20210520214737.MrGGKbPrJ%akpm@linux-foundation.org
Petr Mladek (3): kthread_worker: Split code for canceling the delayed work timer. kthread: Prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync() kthread_worker: Fix return value when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync()
kernel/kthread.c | 96 +++++++++++++++++++++++++++++++----------------- 1 file changed, 63 insertions(+), 33 deletions(-)
-- 2.26.2
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