On 10/4/22 2:59 AM, Fiona Ebner wrote: > Am 26.08.22 um 10:21 schrieb Fiona Ebner: >> Am 11.07.22 um 15:40 schrieb Fabian Ebner: >>> Am 09.07.22 um 05:39 schrieb Shyam Prasad N: >>>> On Sat, Jul 9, 2022 at 9:00 AM Shyam Prasad N <nspmangalore@xxxxxxxxx> wrote: >>>>> >>>>> On Fri, Jul 8, 2022 at 11:22 PM Enzo Matsumiya <ematsumiya@xxxxxxx> wrote: >>>>>> >>>>>> On 07/08, Fabian Ebner wrote: >>>>>>> (Re-sending without the log from the older kernel, because the mail hit >>>>>>> the 100000 char limit with that) >>>>>>> >>>>>>> Hi, >>>>>>> it seems that in kernels >= 5.15, io_uring and CIFS don't interact >>>>>>> nicely sometimes, leading to IO errors. Unfortunately, my reproducer is >>>>>>> a QEMU VM with a disk on CIFS (original report by one of our users [0]), >>>>>>> but I can try to cook up something simpler if you want. >>>>>>> >>>>>>> Bisecting got me to 8ef12efe26c8 ("io_uring: run regular file >>>>>>> completions from task_work") being the first bad commit. >>>>>>> >> >> I finally got around to taking another look at this issue (still present >> in 5.19.3) and I think I've finally figured out the root cause: >> >> After commit 8ef12efe26c8, for my reproducer, the write completion is >> added to task_work with notify_method being TWA_SIGNAL and thus >> TIF_NOTIFY_SIGNAL is set for the task. >> >> After that, if we end up in sk_stream_wait_memory() via sock_sendmsg(), >> signal_pending(current) will evaluate to true and thus -EINTR is >> returned all the way up to sock_sendmsg() in smb_send_kvec(). >> >> Related: in __smb_send_rqst() there too is a signal_pending(current) >> check leading to the -ERESTARTSYS return value. >> >> To verify that this is the cause, I wasn't able to trigger the issue >> anymore with this hack applied (i.e. excluding the TIF_NOTIFY_SIGNAL check): >> >>> diff --git a/net/core/stream.c b/net/core/stream.c >>> index 06b36c730ce8..58e3825930bb 100644 >>> --- a/net/core/stream.c >>> +++ b/net/core/stream.c >>> @@ -134,7 +134,7 @@ int sk_stream_wait_memory(struct sock *sk, long *timeo_p) >>> goto do_error; >>> if (!*timeo_p) >>> goto do_eagain; >>> - if (signal_pending(current)) >>> + if (task_sigpending(current)) >>> goto do_interrupted; >>> sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk); >>> if (sk_stream_memory_free(sk) && !vm_wait) >> >> >> In __cifs_writev() we have >> >>> /* >>> * If at least one write was successfully sent, then discard any rc >>> * value from the later writes. If the other write succeeds, then >>> * we'll end up returning whatever was written. If it fails, then >>> * we'll get a new rc value from that. >>> */ >> >> so it can happen that collect_uncached_write_data() will (correctly) >> report a short write when calling ctx->iocb->ki_complete(). >> >> But QEMU's io_uring backend treats a short write as an -ENOSPC error, >> which also is a bug? Or does the kernel give any guarantees in that >> direction? >> >> Still, it doesn't seem ideal that the "interrupt" happens and in fact >> __smb_send_rqst() tries to avoid it, but fails to do so, because of the >> unexpected TIF_NOTIFY_SIGNAL: >>> /* >>> * We should not allow signals to interrupt the network send because >>> * any partial send will cause session reconnects thus increasing >>> * latency of system calls and overload a server with unnecessary >>> * requests. >>> */ >>> >>> sigfillset(&mask); >>> sigprocmask(SIG_BLOCK, &mask, &oldmask); >> >> Do you have any suggestions for how to proceed? >> > > Ping. The issue is still present in Linux 6.0. Does it make sense to > also temporarily unset the task's TIF_NOTIFY_SIGNAL here or is that a > bad idea? You could try setting up with ring with IORING_SETUP_COOP_TASKRUN, that'll avoid the TIF_NOTIFY_SIGNAL bits. -- Jens Axboe