Re: [syzbot] [mm?] possible deadlock in gup_fast_fallback (3)

Re: [syzbot] [mm?] possible deadlock in gup_fast_fallback (3)

[David Hildenbrand (Arm)]

On 5/12/26 14:48, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    63751099502d Merge branch 'net-mlx5-steering-misc-enhancem..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=1714fbce580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f2b487b72ffad035
> dashboard link: https://syzkaller.appspot.com/bug?extid=8edc46c9c781c802acf4
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1f8de738e2f8/disk-63751099.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ae6cfb0d3b70/vmlinux-63751099.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f00e218e1a55/bzImage-63751099.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+8edc46c9c781c802acf4@syzkaller.appspotmail.com
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Not tainted
> ------------------------------------------------------
> syz.4.2801/16593 is trying to acquire lock:
> ffff88802ae527f8 (&mm->mmap_lock){++++}-{4:4}, at: gup_fast_fallback+0x20d/0x20d0 mm/gup.c:3193
> 
> but task is already holding lock:
> ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
> ffff888055ac9d60 (sk_lock-AF_INET6){+.+.}-{0:0}, at: tls_sw_sendmsg+0x15d/0x2430 net/tls/tls_sw.c:1291
> 
> which lock already depends on the new lock.

I don't know what going on here, but I know for sure that GUP is not to blame ;)

-- 
Cheers,

David