On Tue, Aug 11, 2020 at 08:21:12AM -0600, Jens Axboe wrote: > On 8/11/20 8:00 AM, Stefano Garzarella wrote: > > On Mon, Aug 10, 2020 at 09:55:17AM -0600, Jens Axboe wrote: > >> On 8/10/20 9:36 AM, syzbot wrote: > >>> Hello, > >>> > >>> syzbot found the following issue on: > >>> > >>> HEAD commit: 449dc8c9 Merge tag 'for-v5.9' of git://git.kernel.org/pub/.. > >>> git tree: upstream > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=14d41e02900000 > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=9d25235bf0162fbc > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=996f91b6ec3812c48042 > >>> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=133c9006900000 > >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1191cb1a900000 > >>> > >>> IMPORTANT: if you fix the issue, please add the following tag to the commit: > >>> Reported-by: syzbot+996f91b6ec3812c48042@xxxxxxxxxxxxxxxxxxxxxxxxx > >> > >> Thanks, the below should fix this one. > > > > Yeah, it seems right to me, since only __io_queue_deferred() (invoked by > > io_commit_cqring()) can be called with 'completion_lock' held. > > Right > > > Just out of curiosity, while exploring the code I noticed that we call > > io_commit_cqring() always with the 'completion_lock' held, except in the > > io_poll_* functions. > > > > That's because then there can't be any concurrency? > > Do you mean the iopoll functions? Because we're definitely holding it > for the io_poll_* functions. Right, the only one seems io_iopoll_complete(). So, IIUC, in this case we are actively polling the level below, so there shouldn't be any asynchronous events, is it right? Thanks, Stefano
