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b=fmTqMnAnhE9MOQVMZGc6GAWJwWjXK6gBcrGIx41yQkcCHPnRXov3BlnBkRPb2SylN ejkqoamBQ9/bhx0/0UlAt5D6prU8gPF1YKkf+Olqh3INdN5V7v7vbs7beX3oXWsaiI P/5RU//VTFaaou6jv15Kvoi4rsP5DeW4aPLJAgPEGJfLMKXjiiOhkqb/E5BNtldwT5 rY6xeVAnVAOF4O8TknBX+WGmNT90q/38MylReFStbNQWnwZr18q/rf68hEf18MhW6L iYPNXtgSBBYh4i3IgTIoRRvoDLo+QsqoUQZFz598kLj/oGPUqDT20XuYmTcLLgvdsy KvpCJTAWzZ03w== Message-ID: <1995ce75-68d9-6205-6e8a-ca7c089a93fd@kernel.org> Date: Wed, 5 Jan 2022 23:25:03 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Content-Language: en-US To: Greg KH References: <20220104130513.3077-1-chao@kernel.org> <53d75d26-2289-a66a-a7fa-62593bad81c8@kernel.org> From: Chao Yu In-Reply-To: X-Headers-End: 1n58A6-0033Xg-9w Subject: Re: [f2fs-dev] [PATCH] f2fs: quota: fix potential deadlock X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jaegeuk@kernel.org, Yi Zhuang , stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On 2022/1/5 23:01, Greg KH wrote: > On Tue, Jan 04, 2022 at 11:48:25PM +0800, Chao Yu wrote: >> On 2022/1/4 23:17, Greg KH wrote: >>> On Tue, Jan 04, 2022 at 11:05:36PM +0800, Chao Yu wrote: >>>> On 2022/1/4 21:18, Greg KH wrote: >>>>> On Tue, Jan 04, 2022 at 09:05:13PM +0800, Chao Yu wrote: >>>>>> commit a5c0042200b28fff3bde6fa128ddeaef97990f8d upstream. >>>>>> >>>>>> As Yi Zhuang reported in bugzilla: >>>>>> >>>>>> https://bugzilla.kernel.org/show_bug.cgi?id=214299 >>>>>> >>>>>> 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. >>>>>> >>>>>> Fixes: db6ec53b7e03 ("f2fs: add a rw_sem to cover quota flag changes") >>>>>> Cc: stable@vger.kernel.org # v5.3+ >>>>>> Reported-by: Yi Zhuang >>>>>> Signed-off-by: Chao Yu >>>>>> Signed-off-by: Jaegeuk Kim >>>>>> --- >>>>>> fs/f2fs/checkpoint.c | 3 ++- >>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c >>>>>> index 83e9bc0f91ff..7b0282724231 100644 >>>>>> --- a/fs/f2fs/checkpoint.c >>>>>> +++ b/fs/f2fs/checkpoint.c >>>>>> @@ -1162,7 +1162,8 @@ static bool __need_flush_quota(struct f2fs_sb_info *sbi) >>>>>> if (!is_journalled_quota(sbi)) >>>>>> return false; >>>>>> - down_write(&sbi->quota_sem); >>>>>> + if (!down_write_trylock(&sbi->quota_sem)) >>>>>> + return true; >>>>>> if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) { >>>>>> ret = false; >>>>>> } else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) { >>>>>> -- >>>>>> 2.32.0 >>>>>> >>>>> >>>>> What stable tree(s) is this for? >>>> >>>> Oh, please help to try applying to 5.4, 5.10, and 5.15 stable trees, thanks! >>> >>> This is already in the 5.15.6 kernel release, do you need it applied >>> there again? :) >> >> Oops, no, so 5.4 and 5.10 is enough. ;) >> We can skip 5.15 since this patch was merged in 5.15-rc1 at the first time. > > It was merged in 5.16-rc1, and then backported to 5.15.6. You might > want to check your git scripts. Oh, yes, you're right, it looks we merged patches with same title in both 5.15-rc1 and 5.16-rc1, that won't happen usually... so I positioning the wrong merge time only based on patch title... https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=a5c0042200b28fff3bde6fa128ddeaef97990f8d https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=9de71ede81e6d1a111fdd868b2d78d459fa77f80 > > Anyway, now queued up, thanks. Thank you! Thanks, > > greg k-h _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel