Date: Thu, 8 Apr 2010 11:57:10 +0200 From: Attilio Rao <attilio@freebsd.org> To: Jilles Tjoelker <jilles@stack.nl> Cc: Ed Maste <emaste@sandvine.com>, freebsd-arch@freebsd.org Subject: Re: so_rcv_sx, deadlkres, SIGSTOP Message-ID: <q2s3bbf2fe11004080257t8eeccb1dhdf90913dee28bc2f@mail.gmail.com> In-Reply-To: <20100404175140.GB40499@stack.nl> References: <20100404175140.GB40499@stack.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
2010/4/4 Jilles Tjoelker <jilles@stack.nl>: > The SX locks so_snd_sx and so_rcv_sx can be legitimately held for > arbitrary amounts of time, while waiting until a send or recv is > possible. Any other threads wanting to send/recv on the socket will > sleep interruptibly on the corresponding SX. If deadlkres is activated, > it may detect a deadlock even though there is no problem. > > If a SIGSTOP or similar comes in while waiting until send/recv is > possible, the SX is held across the suspension and noone will be able to > send/recv on the socket until the process is resumed. On the other hand > a thread waiting for the SX can be suspended without harm. Adding PBDRY > to various sleeps may help but may also introduce other problems > (SIGSTOP disturbing the functioning of the process more, possibly with > stuff like SO_RCVTIMEO). > > Example (using the fact that fifos are implemented using sockets): > > term1% mkfifo testfifo > term1% cat >testfifo > > term2% cat testfifo > > term3% cat testfifo > > Letting this sit for half an hour will trigger deadlkres. Jilles, may you please try this patch?: http://www.freebsd.org/~attilio/Sandvine/deadlkres/deadlkres-blessed.diff It does introduce a blessed list where the sx_lock can be whitelisted. It also fixes, for long sleeps, the wrap-up of ticks object. The obvious fallout is that deadlkres can't help much with deadlocks for whitelisted sxlock or lockmgr but that is a fair price I think. Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?q2s3bbf2fe11004080257t8eeccb1dhdf90913dee28bc2f>