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Message-ID: <8ee6270b-f496-4a8e-a7da-82040b8847e0@linux.alibaba.com>
Date: Tue, 24 Sep 2024 18:14:14 +0800
From: Joseph Qi <joseph.qi@...ux.alibaba.com>
To: Mohammed Anees <pvmohammedanees2003@...il.com>,
akpm <akpm@...ux-foundation.org>
Cc: Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
syzbot+e0055ea09f1f5e6fabdd@...kaller.appspotmail.com,
ocfs2-devel@...ts.linux.dev,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] ocfs2: Fix deadlock in ocfs2_get_system_file_inode
On 9/24/24 5:32 PM, Mohammed Anees wrote:
> syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].
>
> The scenario is depicted here,
>
> CPU0 CPU1
> lock(&ocfs2_file_ip_alloc_sem_key);
> lock(&osb->system_file_mutex);
> lock(&ocfs2_file_ip_alloc_sem_key);
> lock(&osb->system_file_mutex);
>
> The function calls which could lead to this are:
>
> CPU0
> ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key);
> .
> .
> .
> ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
>
> CPU1 -
> ocfs2_fill_super - lock(&osb->system_file_mutex);
> .
> .
> .
> ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);
>
> This issue can be resolved by making the down_read -> down_read_try
> in the ocfs2_read_virt_blocks.
>
> [1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
>
> Reported-and-tested-by: syzbot+e0055ea09f1f5e6fabdd@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
> Signed-off-by: Mohammed Anees <pvmohammedanees2003@...il.com>
Cc: <stable@...r.kernel.org>
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> ---
> v3:
> - Removed multiple if conditions
> ---
> fs/ocfs2/extent_map.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
> index 70a768b62..f7672472f 100644
> --- a/fs/ocfs2/extent_map.c
> +++ b/fs/ocfs2/extent_map.c
> @@ -973,7 +973,13 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
> }
>
> while (done < nr) {
> - down_read(&OCFS2_I(inode)->ip_alloc_sem);
> + if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
> + rc = -EAGAIN;
> + mlog(ML_ERROR,
> + "Inode #%llu ip_alloc_sem is temporarily unavailable\n",
> + (unsigned long long)OCFS2_I(inode)->ip_blkno);
> + break;
> + }
> rc = ocfs2_extent_map_get_blocks(inode, v_block + done,
> &p_block, &p_count, NULL);
> up_read(&OCFS2_I(inode)->ip_alloc_sem);
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