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

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Message-ID: <ZcbHTYLSO7mU0e9G@dread.disaster.area>
Date: Sat, 10 Feb 2024 11:46:05 +1100
From: Dave Chinner <david@...morbit.com>
To: Kemeng Shi <shikemeng@...weicloud.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 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....

-Dave.
-- 
Dave Chinner
david@...morbit.com