[PATCH] ubi: Fix deadlock caused by recursively holding work_sem

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1 at 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 at huawei.com>
>> ---
>>   drivers/mtd/ubi/wl.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Reviewed-by: Zhihao Cheng <chengzhihao1 at huawei.com>

Applied to -next. Thanks everyone!

Thanks,
//richard