Re: [syzbot] [rdma?] INFO: task hung in add_one_compat_dev (3)

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Aug 07, 2026 at 06:46:21AM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    f9a2394a2348 Merge tag 'mm-hotfixes-stable-2026-08-06-18-4..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d50fb9580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8e21dcbdb02d4229
> dashboard link: https://syzkaller.appspot.com/bug?extid=6dee15fdb0606ef7b6ba
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14d037b9580000

So this looks like it is just "really slow" beacuse of the vast
amount of work it is triggering in the kernel to manage sysfs files
under locks and the high number of threads running on the same
serializing mutex.

The only way we could do anything about it is to split up the locking
somewhat to be more fine grained, but that seems tricky and
complicated and might trigger a higher level lock anyhow..

I'm not inclined to do that just to silence syzkallers rather
agressive test..

Jason