linux-kernel - Re: [PATCH 1/1] fs-writeback: Using spin_lock to check for work

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Message-ID: <CALN+fr3Vw5yJn2yDMdF=pg1PFziMeZCkYzj_mBzgu+U-10qEKg@mail.gmail.com>
Date:	Wed, 31 Aug 2011 12:21:04 +0530
From:	Rajan Aggarwal <rajan.aggarwal85@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/1] fs-writeback: Using spin_lock to check for work_list empty

Hi Andrew,

Can you please review the patch below and tell me whether it is
technically correct ?

Or, can you please suggest a suitable change for solving this ?

Thanks.
Rajan.


> On Wed, Aug 31, 2011 at 10:41 AM, Rajan Aggarwal
> <rajan.aggarwal85@...il.com> wrote:
>> The bdi_writeback_thread function does not use spin_lock to
>> see if the work_list is empty.
>>
>> If the list is not empty, and if an interrupt happens before we
>> set the current->state to TASK_RUNNING then we could be stuck in
>> a schedule() due to kernel preemption.
>>
>> This patch acquires and releases the wb_lock to avoid this scenario.
>>
>> Signed-off-by: Rajan Aggarwal <rajan.aggarwal85@...il.com>
>> ---
>>  fs/fs-writeback.c |    3 +++
>>  1 files changed, 3 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> index 04cf3b9..e333898 100644
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -936,11 +936,14 @@ int bdi_writeback_thread(void *data)
>>                if (pages_written)
>>                        wb->last_active = jiffies;
>>
>> +               spin_lock_bh(&bdi->wb_lock);
>>                set_current_state(TASK_INTERRUPTIBLE);
>>                if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
>>                        __set_current_state(TASK_RUNNING);
>> +                       spin_unlock_bh(&bdi->wb_lock);
>>                        continue;
>>                }
>> +               spin_unlock_bh(&bdi->wb_lock);
>>
>>                if (wb_has_dirty_io(wb) && dirty_writeback_interval)
>>                        schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
>> --
>> 1.7.4.1
>>
>>
>
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