On Wed, Jun 18, 2008 at 1:07 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > On Tue, 10 Jun 2008 21:27:07 +0100 > "Daniel J Blueman" <daniel.blueman@xxxxxxxxx> wrote: > >> On Tue, Jun 10, 2008 at 8:18 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: >> > On Tue, 10 Jun 2008 15:13:57 -0400 >> > Jeff Layton <jlayton@xxxxxxxxxx> wrote: >> > >> >> On Tue, 10 Jun 2008 14:54:48 -0400 >> >> Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: >> >> >> >> > On Wed, 2008-06-04 at 20:35 -0400, Jeff Layton wrote: >> >> > > On Thu, 5 Jun 2008 00:33:54 +0100 >> >> > > "Daniel J Blueman" <daniel.blueman@xxxxxxxxx> wrote: >> >> > > >> >> > > > Having experienced 'mount.nfs4: internal error' when mounting nfsv4 in >> >> > > > the past, I have a minimal test-case I sometimes run: >> >> > > > >> >> > > > $ while :; do mount -t nfs4 filer:/store /store; umount /store; done >> >> > > > >> >> > > > After ~100 iterations, I saw the 'mount.nfs4: internal error', >> >> > > > followed by symptoms of memory corruption [1], a locking issue with >> >> > > > the reporting [2] and another (related?) memory-corruption issue >> >> > > > (off-by-1?) [3]. A little analysis shows memory being overwritten by >> >> > > > (likely) a poison value, which gets complicated if it's not >> >> > > > use-after-free... >> >> > > > >> >> > > > Anyone dare confirm this issue? NFSv4 server is x86-64 Ubuntu 8.04 >> >> > > > 2.6.24-18, client U8.04 2.6.26-rc4; batteries included [4]. >> >> > > > >> >> > > > I'm happy to decode addresses, test patches etc. >> >> > > > >> >> > > > Daniel >> >> > > > >> >> > > >> >> > > Looks like it fell down while trying to take down the kthread during a >> >> > > failed mount attempt. I have to wonder if I might have introduced a >> >> > > race when I changed nfs4 callback thread to kthread API. I think we may >> >> > > need the BKL around the last 2 statements in the main callback thread >> >> > > function. If you can easily reproduce this, could you test the >> >> > > following patch and let me know if it helps? >> >> > > >> >> > > Note that this patch is entirely untested, so test it someplace >> >> > > non-critical ;-). >> >> > > >> >> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> >> >> > > >> >> > > >> >> > > diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c >> >> > > index c1e7c83..a3e83f9 100644 >> >> > > --- a/fs/nfs/callback.c >> >> > > +++ b/fs/nfs/callback.c >> >> > > @@ -90,9 +90,9 @@ nfs_callback_svc(void *vrqstp) >> >> > > preverr = err; >> >> > > svc_process(rqstp); >> >> > > } >> >> > > - unlock_kernel(); >> >> > > nfs_callback_info.task = NULL; >> >> > > svc_exit_thread(rqstp); >> >> > > + unlock_kernel(); >> >> > > return 0; >> >> > > } >> >> > >> >> > We certainly need to protect nfs_callback_info.task (and I believe I >> >> > explained this earlier), but why do we need to protect svc_exit_thread? >> >> > >> >> > Also, looking at the general use of the BKL in that code, I thought we >> >> > agreed that there was no need to hold the BKL while taking the >> >> > nfs_callback_mutex? >> >> > >> >> >> >> Hmm, I don't remember that discussion, but I'll take your word for it... >> >> >> >> I think you're basically correct, but it looks to me like the >> >> nfs_callback_mutex actually protects nfs_callback_info.task as well. >> >> >> >> If we're starting the thread, then we can't call kthread_stop on it >> >> until we release the mutex. So the thread can't exit until we release >> >> the mutex, and we can be guaranteed that this: >> >> >> >> nfs_callback_info.task = NULL; >> >> >> >> ...can't happen until after kthread_run returns and nfs_callback_up >> >> sets it. >> >> >> >> If that's right, then maybe this (untested, RFC only) patch would make sense? >> >> >> > >> > To clarify for Dan... >> > >> > I don't think that this patch will help the problem you're having. This >> > is essentially a cleanup patch to remove some locking that doesn't >> > appear to be needed. >> > >> > The original patch that Trond commented on above is also probably >> > unnecessary (assuming I'm right about the locking here). >> >> Thanks for the head-up, Jeff. I took it at face value, so didn't >> harbour the notion it would fix the memory corruption. >> >> Let's see If I can get time for this git bisect sooner rather than later... > > I've tried reproducing this, but haven't had much success (probably some > differences in my kernel config). > > I suspect that Trond is correct here and the race has something to > do with the kthread being spawned but nfs_callback_svc() never getting > a chance to run. I posted a patchset to the list late last week with the > intro email: > > [PATCH 0/3] fix potential races in lockd and nfs4-callback startup/shutdown > > Dan, could you apply that patchset to your kernel and see if it helps > this problem? Yes, I confirm the problem reproduces without this patchset and I'm unable to reproduce it with the patchset, so looks good! Thanks again for the all the help and fixes! Dan -- Daniel J Blueman -- 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
