netdev - Re: [PATCH] af_unix: Revert 'lock_interruptible' in stream receive code

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Date:	Thu, 17 Dec 2015 16:43:55 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH] af_unix: Revert 'lock_interruptible' in stream receive
 code

On 17.12.2015 16:28, Rainer Weikusat wrote:
> Hannes Frederic Sowa <hannes@...essinduktion.org> writes:
>> On 16.12.2015 21:09, Rainer Weikusat wrote:
>>> With b3ca9b02b00704053a38bfe4c31dbbb9c13595d0, the AF_UNIX SOCK_STREAM
>>> receive code was changed from using mutex_lock(&u->readlock) to
>>> mutex_lock_interruptible(&u->readlock) to prevent signals from being
>>> delayed for an indefinite time if a thread sleeping on the mutex
>>> happened to be selected for handling the signal. But this was never a
>>> problem with the stream receive code (as opposed to its datagram
>>> counterpart) as that never went to sleep waiting for new messages with the
>>> mutex held and thus, wouldn't cause secondary readers to block on the
>>> mutex waiting for the sleeping primary reader. As the interruptible
>>> locking makes the code more complicated in exchange for no benefit,
>>> change it back to using mutex_lock.
>>>
>>> Signed-off-by: Rainer Weikusat <rweikusat@...ileactivedefense.com>
>>> ---
>>>
>>> Considering that the datagram receive routine also doesn't go the sleep
>>> with the mutex held anymore, the 37ab4fa7844a044dc21fde45e2a0fc2f3c3b6490
>>> change to unix_autobind is now similarly purposeless.
>>
>> I wouldn't do this conversion, yet. There is still a deadlock lingering
>> around which should be solved earlier:
>>
>> http://lists.openwall.net/netdev/2015/11/10/4
>>
>> Unfortunately I haven't found a good way how to solve it, yet.
> 
> Judging from the link, that's not related to the stream receive code.
> 

No, but to commit 37ab4fa7844a044dc21fde45e2a0fc2f3c3b6490 where the
mutexes of unix_bind and unix_autobind got changed.

The unix_stream_read_generic conversion is fine.

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Thanks,
Hannes

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