Re: [PATCH] nbd: fix circular lock dependency

[Bart Van Assche <bvanassche@acm.org>]

On 11/11/26 3:38 AM, Guilherme Giacomo Simoes wrote:
 > After tested, how can I mention this in my patch?

If syzbot confirms the fix, you can either:
- Add a "Tested-by: syzbot..." tag if syzkaller provides one, or
- Mention it below the "---" separator in your patch (in the changelog/notes
   section), e.g.:
   Tested against syzbot reproducer via #syz test: <link-to-syzbot-result>

 > What do you think now? We will call nbd_reclassify_socket() inside
 > nbd_get_socket() and call this only one time? Or is a better way call the
 > nbd_reclassify_socket() inside nbd_genl_reconnect_sock_cb() when we 
have sure
 > that we will use the socket?

Calling nbd_reclassify_socket(sock) directly inside
nbd_genl_reconnect_sock_cb() (right after nbd_get_socket()) is definitely
the best approach:
1. It is a 1-line addition to nbd_genl_reconnect_sock_cb().
2. It mirrors what nbd_add_socket() already does.
3. No code needs to be moved around, keeping the git diff minimal and making
    the fix trivial to review and backport to stable kernels.

 > What do you think:
 > ```
 > nbd: must reclassify socket when socket is created
 >
 > When we need to connect or reconnect a new socket, we need to call
 > nbd_reclassify_socket() to ensure that a false positive lock_dep
 > circular warning fires. [...]
 > ```

Please use the imperative mood, e.g. as follows:

nbd: Reclassify sockets in the reconnect path

Commit d532cddb6c60 ("nbd: Reclassify sockets to avoid lockdep circular 
dependency") introduced nbd_reclassify_socket() to prevent lockdep false 
positives when NBD sockets are used in memory reclaim paths. While 
nbd_add_socket() reclassifies newly added sockets, 
nbd_genl_reconnect_sock_cb() omitted this call when replacing dead 
sockets during reconnection. Consequently, reconnected sockets retain 
the generic socket lockdep class and trigger false-positive lockdep reports.

Fix this by reclassifying the replacement socket in 
nbd_genl_reconnect_sock_cb().

Fixes: d532cddb6c60 ("nbd: Reclassify sockets to avoid lockdep circular 
dependency")
Reported-by: syzbot+d7d72f3d467710442af0@syzkaller.appspotmail.com 
Closes: https://syzkaller.appspot.com/bug?extid=d7d72f3d467710442af0



Thanks,

Bart.