linux-kernel - Re: [PATCH 4/7] fs/writeback: remove unneeded check in writeback_single

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Date: Sun, 18 Feb 2024 10:37:36 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: Dave Chinner <david@...morbit.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] fs/writeback: remove unneeded check in
 writeback_single_inode



on 2/10/2024 8:46 AM, Dave Chinner wrote:
> On Fri, Feb 09, 2024 at 01:20:21AM +0800, Kemeng Shi wrote:
>> I_DIRTY_ALL consists of I_DIRTY_TIME and I_DIRTY, so I_DIRTY_TIME must
>> be set when any bit of I_DIRTY_ALL is set but I_DIRTY is not set.
>>
>> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
>> ---
>>  fs/fs-writeback.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> index 2619f74ced70..b61bf2075931 100644
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -1788,7 +1788,7 @@ static int writeback_single_inode(struct inode *inode,
>>  		else if (!(inode->i_state & I_SYNC_QUEUED)) {
>>  			if ((inode->i_state & I_DIRTY))
>>  				redirty_tail_locked(inode, wb);
>> -			else if (inode->i_state & I_DIRTY_TIME) {
>> +			else {
>>  				inode->dirtied_when = jiffies;
>>  				inode_io_list_move_locked(inode,
>>  							  wb,
> 
> NAK.
> 
> The code is correct and the behaviour that is intended it obvious
> from the code as it stands.
> 
> It is -incorrect- to move any inode that does not have I_DIRTY_TIME
> to the wb->b_dirty_time list. By removing the I_DIRTY_TIME guard
> from this code, you are leaving a nasty, undocumented logic trap in
> the code that somebody is guaranteed to trip over into in the
> future. That's making the code worse, not better....
Sure, I will remove this one in next version. Thanks for the
explanation.
> 
> -Dave.
>