Date:   Sat, 4 Mar 2023 17:59:41 +0100 (CET)
From:   Richard Weinberger <richard@nod.at>
To:     chengzhihao1 <chengzhihao1@huawei.com>
Cc:     ZhaoLong Wang <wangzhaolong1@huawei.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        yi zhang <yi.zhang@huawei.com>
Message-ID: <1472678614.203878.1677949181290.JavaMail.zimbra@nod.at>
In-Reply-To: <2d3b033a-5329-be95-fe38-2cceb17b9014@huawei.com>
References: <20230304014141.2099204-1-wangzhaolong1@huawei.com> <2d3b033a-5329-be95-fe38-2cceb17b9014@huawei.com>
Subject: Re: [PATCH] ubi: Fix deadlock caused by recursively holding
 work_sem
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Thread-Topic: Fix deadlock caused by recursively holding work_sem
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----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@huawei.com>
>> During the processing of the bgt, if the sync_erase() return -EBUSY
>> or some other error code in __erase_worker(),schedule_erase() called
>> again lead to the down_read(ubi->work_sem) hold twice and may get
>> block by down_write(ubi->work_sem) in ubi_update_fastmap(),
>> which cause deadlock.
>> 
>>            ubi bgt                        other task
>>   do_work
>>    down_read(&ubi->work_sem)          ubi_update_fastmap
>>    erase_worker                         # Blocked by down_read
>>     __erase_worker                      down_write(&ubi->work_sem)
>>      schedule_erase
>>       schedule_ubi_work
>>        down_read(&ubi->work_sem)
>> 
>> Fix this by changing input parameter @nested of the schedule_erase() to
>> 'true' to avoid recursively acquiring the down_read(&ubi->work_sem).
>> 
>> Also, fix the incorrect comment about @nested parameter of the
>> schedule_erase() because when down_write(ubi->work_sem) is held, the
>> @nested is also need be true.
>> 
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217093
>> Fixes: 2e8f08deabbc ("ubi: Fix races around ubi_refill_pools()")
>> Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
>> ---
>>   drivers/mtd/ubi/wl.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>

Applied to -next. Thanks everyone!

Thanks,
//richard