Messages in this thread | | | From | Shachar Raindel <> | Date | Thu, 30 Dec 2021 17:06:23 -0800 | Subject | Re: [f2fs-dev] [PATCH] f2fs: quota: fix potential deadlock |
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Somewhat late to the party (i.e. 3 months late), happy mailbox cleanup holidays!
On Thu, Sep 2, 2021 at 8:04 PM Chao Yu <chao@kernel.org> wrote: > > As Yi Zhuang reported in bugzilla: > > https://bugzilla.kernel.org/show_bug.cgi?id=214299 > Bug report is for kernel 5.3. When I reported very similar deadlock in google-msm 4.9 tree ( https://lore.kernel.org/linux-f2fs-devel/20201128174124.22397-1-shacharr@gmail.com/t/ ), you pointed out that the code was missing commits which removed the cp_rwsem grabbing (which are also missing from kernel 5.3):
commit 435cbab95e3966cd8310addd9e9b758dce0e8b84 Author: Jaegeuk Kim <jaegeuk@kernel.org> Date: Thu Apr 9 10:25:21 2020 -0700
f2fs: fix quota_sync failure due to f2fs_lock_op
commit ca7f76e680745d3b8a386638045f85dac1c4b2f4 Author: Chao Yu <chao@kernel.org> Date: Fri May 29 17:29:47 2020 +0800
f2fs: fix wrong discard space
commit 79963d967b492876fa17c8c2c2c17b7438683d9b Author: Chao Yu <chao@kernel.org> Date: Thu Jun 18 14:36:23 2020 +0800
f2fs: shrink node_write lock coverage
Is this patch needed with these commits applied?
> > There is potential deadlock during quota data flush as below: > > Thread A: Thread B: > f2fs_dquot_acquire > down_read(&sbi->quota_sem) > f2fs_write_checkpoint > block_operations > f2fs_look_all > down_write(&sbi->cp_rwsem) > f2fs_quota_write > f2fs_write_begin > __do_map_lock > f2fs_lock_op > down_read(&sbi->cp_rwsem) > __need_flush_qutoa > down_write(&sbi->quota_sem) > > This patch changes block_operations() to use trylock, if it fails, > it means there is potential quota data updater, in this condition, > let's flush quota data first and then trylock again to check dirty > status of quota data. > > The side effect is: in heavy race condition (e.g. multi quota data > upaters vs quota data flusher), it may decrease the probability of > synchronizing quota data successfully in checkpoint() due to limited > retry time of quota flush. > > Reported-by: Yi Zhuang <zhuangyi1@huawei.com> > Signed-off-by: Chao Yu <chao@kernel.org>
As this patch is applied in the mainline kernel, can we CC -stable to get this patch into the various Android kernels? Specifically, https://android.googlesource.com/kernel/msm/+/refs/tags/android-12.0.0_r0.21/fs/f2fs/checkpoint.c#1147 needs this patch (alongside many other google-msm kernel branches).
Thanks, --Shachar
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