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[59.102.81.67]) by smtp.gmail.com with ESMTPSA id j16-v6sm2721797pfk.125.2018.08.28.07.35.43 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 28 Aug 2018 07:35:46 -0700 (PDT) Date: Wed, 29 Aug 2018 00:35:39 +1000 From: Nicholas Piggin To: Matteo Croce Cc: Greg Kroah-Hartman , Jiri Slaby , Michael Ellerman , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org Subject: Re: VirtIO console hangs Message-ID: <20180829003539.668e514c@roar.ozlabs.ibm.com> In-Reply-To: References: X-Mailer: Claws Mail 3.17.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Aug 2018 12:54:08 +0000 Matteo Croce wrote: > With kernel 4.19.0-rc1 virtio_console hangs very often. > I can always trigger the bug by pasting some characters in the > terminal window, the console will stop receiving keypresses, but I can > still see output from the console. > Stangely, logging in the VM via SSH and sending lot of data to hvc0, > like 'dmesg >/dev/hvc0' will fix the issue until the next paste. > > I did a git bisect and I've found that this is the offending commit, > reverting it fixes it. > > Cheers, > > commit ec97eaad1383ab2500fcf9a07ade6044fbcc67f5 > Author: Nicholas Piggin > Date: Tue May 1 00:55:54 2018 +1000 > > tty: hvc: hvc_poll() break hv read loop Thanks for the report. I can't immediately see what the problem is. Can you try get a stack trace of where it is stuck? Perhaps try this patch if you have time (it's a bit of a shot in the dark). Thanks, Nick diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 5414c4a87bea..ac45235832f1 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -635,6 +635,7 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) int read_total = 0; int written_total = 0; +again: spin_lock_irqsave(&hp->lock, flags); /* Push pending writes */ @@ -721,6 +722,10 @@ static int __hvc_poll(struct hvc_struct *hp, bool may_sleep) poll_mask |= HVC_POLL_READ; read_total = n; + spin_unlock_irqrestore(&hp->lock, flags); + cond_resched(); + goto again; + out: /* Wakeup write queue if necessary */ if (hp->do_wakeup) {