linux-ext4 - Re: [PATCH v2] ext4: Fix warning in ext4_dio_write_end

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Message-Id: <87bkbbijwt.fsf@doe.com>
Date: Thu, 30 Nov 2023 16:32:10 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Jan Kara <jack@...e.cz>, Ted Tso <tytso@....edu>
Cc: linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>, syzbot+47479b71cdfc78f56d30@...kaller.appspotmail.com
Subject: Re: [PATCH v2] ext4: Fix warning in ext4_dio_write_end_io()

Jan Kara <jack@...e.cz> writes:

> The syzbot has reported that it can hit the warning in
> ext4_dio_write_end_io() because i_size < i_disksize. Indeed the
> reproducer creates a race between DIO IO completion and truncate
> expanding the file and thus ext4_dio_write_end_io() sees an inconsistent
> inode state where i_disksize is already updated but i_size is not
> updated yet. Since we are careful when setting up DIO write and consider
> it extending (and thus performing the IO synchronously with i_rwsem held
> exclusively) whenever it goes past either of i_size or i_disksize, we
> can use the same test during IO completion without risking entering
> ext4_handle_inode_extension() without i_rwsem held. This way we make it
> obvious both i_size and i_disksize are large enough when we report DIO
> completion without relying on unreliable WARN_ON.
>
> Reported-by: syzbot+47479b71cdfc78f56d30@...kaller.appspotmail.com
> Fixes: 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO")
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
>  fs/ext4/file.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> Changes since v1:
> * Expanded comment in ext4_inode_extension_cleanup()


Looks good to me. Please feel free to add - 

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>