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Mon, 10 Aug 2026 17:06:42 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wta0v-00000002HCN-3XlD; Mon, 10 Aug 2026 21:06:41 -0300 Date: Mon, 10 Aug 2026 21:06:41 -0300 From: Jason Gunthorpe To: syzbot Cc: leon@kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, nogikh@google.com, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [rdma?] INFO: task hung in add_one_compat_dev (3) Message-ID: <20260811000641.GA541676@ziepe.ca> References: <671756af.050a0220.10f4f4.010f.GAE@google.com> <6a75e1ad.b50370da.49fe0.001b.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6a75e1ad.b50370da.49fe0.001b.GAE@google.com> 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