linux-ext4 - Re: [PATCH] ext4: fix semaphore unlocking order

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Message-Id: <87h6goqx9u.fsf@gmail.com>
Date: Sat, 30 Mar 2024 07:46:45 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Mikhail Ukhin <mish.uxin2012@...dex.ru>, Theodore Ts'o <tytso@....edu>
Cc: Mikhail Ukhin <mish.uxin2012@...dex.ru>, Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org, Michail Ivanov <iwanov-23@...ru>, Pavel Koshutin <koshutin.pavel@...dex.ru>, Artem Sadovnikov <ancowi69@...il.com>
Subject: Re: [PATCH] ext4: fix semaphore unlocking order

Mikhail Ukhin <mish.uxin2012@...dex.ru> writes:

> Fuzzing reports a possible deadlock in jbd2_log_wait_commit.
>
> The problem occurs in ext4_ind_migrate due to an incorrect order of
> unlocking of the journal and write semaphores - the order of unlocking
> must be the reverse of the order of locking.
>

Maybe we should update the subject msg to:
      "ext4: "fix i_data_sem unlock order in ext4_ind_migrate()"

and also should add:
    CC: stable@...r.kernel.org


I think this should have been fixed in patch [1], but looks like it
forgot to fix the unlock order.

[1]: https://lore.kernel.org/all/1364801462-13120-1-git-send-email-dmonakhov@openvz.org/


> Found by Linux Verification Center (linuxtesting.org) with syzkaller.

I am not sure if there is an easy reproducer. If yes, we should consider
adding it in fstests.

>
> Signed-off-by: Artem Sadovnikov <ancowi69@...il.com>

Thanks for fixing it. With above changes to subject and CC tag, this
looks good to me. Feel free to add - 

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

> ---
>  fs/ext4/migrate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
> index d98ac2af8199..a5e1492bbaaa 100644
> --- a/fs/ext4/migrate.c
> +++ b/fs/ext4/migrate.c
> @@ -663,8 +663,8 @@ int ext4_ind_migrate(struct inode *inode)
>  	if (unlikely(ret2 && !ret))
>  		ret = ret2;
>  errout:
> -	ext4_journal_stop(handle);
>  	up_write(&EXT4_I(inode)->i_data_sem);
> +	ext4_journal_stop(handle);
>  out_unlock:
>  	ext4_writepages_up_write(inode->i_sb, alloc_ctx);
>  	return ret;
> -- 
> 2.25.1