On 07/02/2015 10:59 AM, Al Viro wrote: > On Thu, Jul 02, 2015 at 10:50:05AM +0300, Andrey Ryabinin wrote: > >>>> and see if it triggers. I'm not sure if failing with ENOMEM is the >>>> right response (another variant is to sleep there until the pile >>>> gets cleaned or until we get killed), and WARN_ON_ONCE() is definitely >>>> not for the real work, but it will do for confirming that this is what >>>> we are hitting. >>> >> >> Apparently, I'm seeing something else. That WARN_ON_ONCE didn't trigger. > > Summary for those who'd missed the beginning of the thread: what we are > seeing is p9_client_write() issing TWRITE and getting RWRITE in reply > (tags match, packets look plausible) with count in RWRITE way more than > that in TWRITE. > > IOW, we are telling the server to write e.g. 93 bytes and are getting told > that yes, the write had been successful - all 4096 bytes of it. > > qemu virtio-9p for server; from my reading of qemu side of things, it can't > be sending reply with count greater than that in request. Besides qemu, I've also tried kvmtool with the same result. IOW I'm seeing this under kvmtool as well. It just takes a bit longer to reproduce this in kvmtool. > The bug I suspected to be the cause of that is in tag allocation in > net/9p/client.c - we could end up wrapping around 2^16 with enough pending > requests and that would have triggered that kind of mess. However, Andrey > doesn't see that test (tag wraparound in p9_client_prepare_req()) trigger. > BTW, was that on the run where debugging printk in p9_client_write() *did* > trigger? Yes, WARN_ON_ONCE() in p9_client_prepare_req() didn't trigger, but debug printk in p9_client_write() *did* trigger. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
