On Mon, Jan 14, 2013 at 03:25:50PM +0000, Myklebust, Trond wrote: > On Mon, 2013-01-14 at 10:09 -0500, Chris Perl wrote: > > On Fri, Jan 11, 2013 at 11:19:44AM -0500, Chris Perl wrote: > > > On Thu, Jan 10, 2013 at 09:30:58PM +0000, Myklebust, Trond wrote: > > > > On Wed, 2013-01-09 at 15:52 -0500, Trond Myklebust wrote: > > > > > On Wed, 2013-01-09 at 12:55 -0500, Chris Perl wrote: > > > > > > > Hrm. I guess I'm in over my head here. Apologoies if I'm just asking > > > > > > > silly bumbling questions. You can start ignoring me at any time. :) > > > > > > > > > > > > I stared at the code for a while and more and now see why what I > > > > > > outlined is not possible. Thanks for helping to clarify! > > > > > > > > > > > > I decided to pull your git repo and compile with HEAD at > > > > > > 87ed50036b866db2ec2ba16b2a7aec4a2b0b7c39 (linux-next as of this > > > > > > morning). Using this kernel, I can no longer induce any hangs. > > > > > > > > > > > > Interestingly, I tried recompiling the CentOS 6.3 kernel with > > > > > > both the original patch (v4) and the last patch you sent about fixing > > > > > > priority queues. With both of those in place, I still run into a > > > > > > problem. > > > > > > > > > > > > echo 0 > /proc/sys/sunrpc/rpc_debug after the hang shows (I left in the > > > > > > previous additional prints and added printing of the tasks pointer > > > > > > itself): > > > > > > > > > > > > <6>client: ffff88082896c200, xprt: ffff880829011000, snd_task: ffff880829a1aac0 > > > > > > <6>client: ffff8808282b5600, xprt: ffff880829011000, snd_task: ffff880829a1aac0 > > > > > > <6>--task-- -pid- flgs status -client- --rqstp- -timeout ---ops-- > > > > > > <6>ffff88082a463180 22007 0080 -11 ffff8808282b5600 (null) 0 ffffffffa027b7a0 nfsv3 ACCESS a:call_reserveresult q:xprt_sending > > > > > > <6>client: ffff88082838cc00, xprt: ffff88082b7c5800, snd_task: (null) > > > > > > <6>client: ffff8808283db400, xprt: ffff88082b7c5800, snd_task: (null) > > > > > > <6>client: ffff8808283db200, xprt: ffff880829011000, snd_task: ffff880829a1aac0 > > > > > > > > > > > > Any thoughts about other patches that might affect this? > > > > > > > > > > Hmm... The only one that springs to mind is this one (see attachment) > > > > > and then the 'connect' fixes that you helped us with previously. > > > > > > > > Never mind. I suspect that the main reason why RHEL-6.3 is still > > > > vulnerable is that it lacks commit > > > > 961a828df64979d2a9faeeeee043391670a193b9 (SUNRPC: Fix potential races in > > > > xprt_lock_write_next()). > > > > > > Great, thanks! I've add this on top of the others and am now testing. > > > I'll let you know how it goes. > > > > With all 4 patches in place, I am no longer able to hang my CentOS 6.3 > > system. I have not tested all the various combinations of the 4 > > patches, but can definitely confirm that without either of: > > > > 961a828df64979d2a9faeeeee043391670a193b9 SUNRPC: Fix potential races in xprt_lock_write_next() > > 87ed50036b866db2ec2ba16b2a7aec4a2b0b7c39 SUNRPC: Ensure we release the socket write lock if the rpc_task exits early > > > > I can hang the system using the test program I sent in my first email. > > > > I'll follow up with Red Hat and ask that they include all 4 patches for > > 6.4 (some of the earlier ones they may already have). > > > > Thanks so much for all the help! > > Likewise. Thank you for all the work you did in debugging and testing. > It is much appreciated. Oh, I had just one other question about the final version of the patch you created. In xprt_release, is it safe to access xprt->snd_task without the transport_lock because of the rcu_lock()/rcu_unlock() stuff, or because all architectures can atomically read pointer sized values that are aligned in certain ways, or something else? -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
