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

Hannes Frederic Sowa [off-list ref] writes:

On 16.12.2015 21:09, Rainer Weikusat wrote:

quoted

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 <redacted>
---

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.

On 17.12.2015 16:28, Rainer Weikusat wrote:

Hannes Frederic Sowa [off-list ref] writes:

quoted

On 16.12.2015 21:09, Rainer Weikusat wrote:

quoted

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 <redacted>
---

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 <redacted>

Thanks,
Hannes