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Mon, 17 Aug 2026 03:53:08 -0700 (PDT) From: Abd-Alrhman Masalkhi To: Zizhi Wo , song@kernel.org, yukuai@fygo.io, magiclinan@didiglobal.com, xiao@kernel.org, linux-raid@vger.kernel.org Cc: linux-kernel@vger.kernel.org, yangerkun@huawei.com, chengzhihao1@huawei.com, wozizhi@huawei.com Subject: Re: [PATCH V2 2/2] md/raid10: fix missing wakeup in wait_barrier_nolock In-Reply-To: <20260817033340.418119-3-wozizhi@huawei.com> References: <20260817033340.418119-1-wozizhi@huawei.com> <20260817033340.418119-3-wozizhi@huawei.com> Date: Mon, 17 Aug 2026 12:53:03 +0200 Message-ID: Precedence: bulk X-Mailing-List: linux-raid@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Mon, Aug 17, 2026 at 11:33 +0800, Zizhi Wo wrote: > [BUG] > Recently, our fuzz testing triggered a hungtask issue in RAID10: > > INFO: task md0_raid10:1273 blocked for more than 120 seconds. > Not tainted 7.2.0-rc6+ #94 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:md0_raid10 state:D stack:0 pid:1273 tgid:1273 ppid:2 > Call Trace: > > __schedule+0xdf9/0x5c90 > ? _raw_spin_unlock_irqrestore+0xe/0x40 > schedule+0x74/0x1f0 > raid10d.cold+0x7db/0x1992 > md_thread+0x1ce/0x3e0 > kthread+0x327/0x410 > ...... > > [CAUSE] > The root cause of the issue is as follows: > [read process1] [read process2] [raid10d] > raid10_make_request > ... > // nr_pending == 1 > atomic_inc(&conf->nr_pending) > ... > raid10_end_read_request > reschedule_retry > md_wakeup_thread(mddev->thread) > raid10_read_request > regular_request_wait > wait_barrier > wait_barrier_nolock > seq = read_seqbegin(&conf->resync_lock) > // nr_pending == 2 > atomic_inc(&conf->nr_pending) > raid10d > handle_read_error > freeze_array > write_seqlock_irq(&conf->resync_lock) > conf->array_freeze_pending++ > WRITE_ONCE(conf->barrier, conf->barrier + 1) > conf->nr_waiting++ > // nr_pending == 2, nr_queued == 0 > wait_event_barrier_cmd > write_sequnlock_irq(&(conf)->resync_lock) > schedule // hungtask!! > read_seqretry(&conf->resync_lock, seq) > // not wakeup because conf->nr_pending == 1 > atomic_dec_and_test(&conf->nr_pending) > /* Hungtask will also occur here: since the barrier is non-zero, > * this I/O can never complete, so it can't call allow_barrier() > * to wake up the pending freeze_array(). */ > wait_event_barrier(conf, stop_waiting_barrier(conf)) > > wait_barrier_nolock() speculatively increments nr_pending and, on a seqlock > retry, rolls it back with atomic_dec_and_test(). The wake fires only when > nr_pending reaches 0. This causes the freeze_array() in the aforementioned > raid10d flow to never be woken up. > > [FIX] > Referring to allow_barrier(), this issue can be fixed by adding a wake-up > condition for "conf->array_freeze_pending" in wait_barrier_nolock(). > > Fixes: b9b083f9044a ("md/raid10: convert resync_lock to use seqlock") > Signed-off-by: Zizhi Wo > --- > drivers/md/raid10.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c > index dc40110a6736..8dadf13c2b4d 100644 > --- a/drivers/md/raid10.c > +++ b/drivers/md/raid10.c > @@ -994,11 +994,12 @@ static bool wait_barrier_nolock(struct r10conf *conf) > > atomic_inc(&conf->nr_pending); > if (!read_seqretry(&conf->resync_lock, seq)) > return true; > > - if (atomic_dec_and_test(&conf->nr_pending)) > + if (atomic_dec_and_test(&conf->nr_pending) || > + READ_ONCE(conf->array_freeze_pending)) > wake_up_barrier(conf); > > return false; > } > > -- > 2.52.0 > > It looks good to me. Reviewed-by: Abd-Alrhman Masalkhi -- Best Regards, Abd-Alrhman