From: Rainer Weikusat <rweiku...@mobileactivedefense.com> Date: Sun, 06 Dec 2015 21:11:38 +0000
> The current unix_dgram_recvsmg code acquires the u->readlock mutex in > order to protect access to the peek offset prior to calling > __skb_recv_datagram for actually receiving data. This implies that a > blocking reader will go to sleep with this mutex held if there's > presently no data to return to userspace. Two non-desirable side effects > of this are that a later non-blocking read call on the same socket will > block on the ->readlock mutex until the earlier blocking call releases it > (or the readers is interrupted) and that later blocking read calls > will wait longer than the effective socket read timeout says they > should: The timeout will only start 'ticking' once such a reader hits > the schedule_timeout in wait_for_more_packets (core.c) while the time it > already had to wait until it could acquire the mutex is unaccounted for. > > The patch avoids both by using the __skb_try_recv_datagram and > __skb_wait_for_more packets functions created by the first patch to > implement a unix_dgram_recvmsg read loop which releases the readlock > mutex prior to going to sleep and reacquires it as needed > afterwards. Non-blocking readers will thus immediately return with > -EAGAIN if there's no data available regardless of any concurrent > blocking readers and all blocking readers will end up sleeping via > schedule_timeout, thus honouring the configured socket receive timeout. > > Signed-Off-By: Rainer Weikusat <rweiku...@mobileactivedefense.com> Also applied to net-next, thanks. BTW, it's "Signed-off-by: ". Only the first word is capitalized. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
