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Mon, 12 Feb 2018 03:34:25 -0500 Date: Mon, 12 Feb 2018 09:34:24 +0100 Message-ID: From: Takashi Iwai To: Ben Hutchings Cc: stable@vger.kernel.org, Greg Kroah-Hartman , LKML Subject: Re: [PATCH 4.4 20/87] ALSA: pcm: Allow aborting mutex lock at OSS read/write loops In-Reply-To: <1516750548.3417.34.camel@codethink.co.uk> References: <20180115123349.252309699@linuxfoundation.org> <20180115123351.309626066@linuxfoundation.org> <1516750548.3417.34.camel@codethink.co.uk> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, 24 Jan 2018 00:35:48 +0100, Ben Hutchings wrote: > > On Mon, 2018-01-15 at 13:34 +0100, Greg Kroah-Hartman wrote: > > 4.4-stable review patch.  If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Takashi Iwai > > > > commit 900498a34a3ac9c611e9b425094c8106bdd7dc1c upstream. > > > > PCM OSS read/write loops keep taking the mutex lock for the whole > > read/write, and this might take very long when the exceptionally high > > amount of data is given.  Also, since it invokes with mutex_lock(), > > the concurrent read/write becomes unbreakable. > > > > This patch tries to address these issues by replacing mutex_lock() > > with mutex_lock_interruptible(), and also splits / re-takes the lock > > at each read/write period chunk, so that it can switch the context > > more finely if requested. > [...] > > @@ -1414,18 +1417,18 @@ static ssize_t snd_pcm_oss_write1(struct > >   xfer += tmp; > >   if ((substream->f_flags & O_NONBLOCK) != 0 && > >       tmp != runtime->oss.period_bytes) > > - break; > > + tmp = -EAGAIN; > >   } > > + err: > > + mutex_unlock(&runtime->oss.params_lock); > > + if (tmp < 0) > > + break; > >   if (signal_pending(current)) { > >   tmp = -ERESTARTSYS; > > - goto err; > > + break; > >   } > > + tmp = 0; > >   } > > - mutex_unlock(&runtime->oss.params_lock); > > - return xfer; > > - > > - err: > > - mutex_unlock(&runtime->oss.params_lock); > >   return xfer > 0 ? (snd_pcm_sframes_t)xfer : tmp; > >  } > [...] > > Some of the "goto err" statements in the loop are conditional on tmp <= > 0, but if tmp == 0 this will no longer terminate the loop. Is that > intentional or a bug? The patch rather fixes the endless loop: the signal_pending() check is added after goto err, so that it aborts the loop properly. thanks, Takashi