* Possible btrfs deadlock coused by commit 660d3f6c
@ 2012-01-16 8:53 Stanislaw Gruszka
2012-01-16 14:26 ` Josef Bacik
0 siblings, 1 reply; 5+ messages in thread
From: Stanislaw Gruszka @ 2012-01-16 8:53 UTC (permalink / raw)
To: Josef Bacik; +Cc: Patrick, linux-btrfs
Hi Josef,
commit 660d3f6cde552323578b85fc5a09a6742f1fe804
Author: Josef Bacik <josef@redhat.com>
Date: Fri Dec 9 11:18:51 2011 -0500
Btrfs: fix how we do delalloc reservations and how we free reservations on error
introduced possible deadlock. According to comment before
btrfs_page_mkwrite(), that function is not allowed to take
node->i_mutex .
The problem was detected by Patrick (full lockdep info is provided):
http://bugzilla.kernel.org/attachment.cgi?id=72072
during investigating of some other issue (kernel.org bug 42576)
Stanislaw
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: Possible btrfs deadlock coused by commit 660d3f6c 2012-01-16 8:53 Possible btrfs deadlock coused by commit 660d3f6c Stanislaw Gruszka @ 2012-01-16 14:26 ` Josef Bacik 2012-01-16 20:45 ` Al Viro 0 siblings, 1 reply; 5+ messages in thread From: Josef Bacik @ 2012-01-16 14:26 UTC (permalink / raw) To: Stanislaw Gruszka; +Cc: Josef Bacik, Patrick, linux-btrfs On Mon, Jan 16, 2012 at 09:53:23AM +0100, Stanislaw Gruszka wrote: > Hi Josef, > > commit 660d3f6cde552323578b85fc5a09a6742f1fe804 > Author: Josef Bacik <josef@redhat.com> > Date: Fri Dec 9 11:18:51 2011 -0500 > > Btrfs: fix how we do delalloc reservations and how we free reservations on error > > introduced possible deadlock. According to comment before > btrfs_page_mkwrite(), that function is not allowed to take > node->i_mutex . > > The problem was detected by Patrick (full lockdep info is provided): > http://bugzilla.kernel.org/attachment.cgi?id=72072 > during investigating of some other issue (kernel.org bug 42576) > It's not a deadlock since you can't mmap a directory, but I posted a fix for this to linux-btrfs last week, afaik it's headed to -rc1. Thanks, Joesf ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Possible btrfs deadlock coused by commit 660d3f6c 2012-01-16 14:26 ` Josef Bacik @ 2012-01-16 20:45 ` Al Viro 2012-01-16 22:01 ` Josef Bacik 0 siblings, 1 reply; 5+ messages in thread From: Al Viro @ 2012-01-16 20:45 UTC (permalink / raw) To: Josef Bacik; +Cc: Stanislaw Gruszka, Patrick, linux-btrfs On Mon, Jan 16, 2012 at 09:26:00AM -0500, Josef Bacik wrote: > On Mon, Jan 16, 2012 at 09:53:23AM +0100, Stanislaw Gruszka wrote: > > Hi Josef, > > > > commit 660d3f6cde552323578b85fc5a09a6742f1fe804 > > Author: Josef Bacik <josef@redhat.com> > > Date: Fri Dec 9 11:18:51 2011 -0500 > > > > Btrfs: fix how we do delalloc reservations and how we free reservations on error > > > > introduced possible deadlock. According to comment before > > btrfs_page_mkwrite(), that function is not allowed to take > > node->i_mutex . > > > > The problem was detected by Patrick (full lockdep info is provided): > > http://bugzilla.kernel.org/attachment.cgi?id=72072 > > during investigating of some other issue (kernel.org bug 42576) > > > > It's not a deadlock since you can't mmap a directory, but I posted a fix for > this to linux-btrfs last week, afaik it's headed to -rc1. Thanks, Sigh... You know, I'm getting really annoyed with the "can't mmap a directory" bogosity resurfacing every couple of months or so. No, you can't mmap a directory. You also can't bugger a hedgehog, which is about as relevant. What you *can* do is write(2) on a regular file. Which will happily grab ->i_mutex (in case of btrfs, that's done in the beginning of btrfs_file_aio_write()) and eventually get the user pages in (in case of btrfs, iov_iter_fault_in_readable() from __btrfs_buffered_write() from btrfs_file_aio_write()). IOW, you do get pagefaults with ->i_mutex held. Which means ->mmap_sem grabbed while holding ->i_mutex. No directories involved... ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Possible btrfs deadlock coused by commit 660d3f6c 2012-01-16 20:45 ` Al Viro @ 2012-01-16 22:01 ` Josef Bacik 2012-01-16 22:35 ` Chris Samuel 0 siblings, 1 reply; 5+ messages in thread From: Josef Bacik @ 2012-01-16 22:01 UTC (permalink / raw) To: Al Viro; +Cc: Josef Bacik, Stanislaw Gruszka, Patrick, linux-btrfs On Mon, Jan 16, 2012 at 08:45:29PM +0000, Al Viro wrote: > On Mon, Jan 16, 2012 at 09:26:00AM -0500, Josef Bacik wrote: > > On Mon, Jan 16, 2012 at 09:53:23AM +0100, Stanislaw Gruszka wrote: > > > Hi Josef, > > > > > > commit 660d3f6cde552323578b85fc5a09a6742f1fe804 > > > Author: Josef Bacik <josef@redhat.com> > > > Date: Fri Dec 9 11:18:51 2011 -0500 > > > > > > Btrfs: fix how we do delalloc reservations and how we free reservations on error > > > > > > introduced possible deadlock. According to comment before > > > btrfs_page_mkwrite(), that function is not allowed to take > > > node->i_mutex . > > > > > > The problem was detected by Patrick (full lockdep info is provided): > > > http://bugzilla.kernel.org/attachment.cgi?id=72072 > > > during investigating of some other issue (kernel.org bug 42576) > > > > > > > It's not a deadlock since you can't mmap a directory, but I posted a fix for > > this to linux-btrfs last week, afaik it's headed to -rc1. Thanks, > > Sigh... You know, I'm getting really annoyed with the "can't mmap a directory" > bogosity resurfacing every couple of months or so. No, you can't mmap a > directory. You also can't bugger a hedgehog, which is about as relevant. > > What you *can* do is write(2) on a regular file. Which will happily grab > ->i_mutex (in case of btrfs, that's done in the beginning of > btrfs_file_aio_write()) and eventually get the user pages in (in case of > btrfs, iov_iter_fault_in_readable() from __btrfs_buffered_write() from > btrfs_file_aio_write()). IOW, you do get pagefaults with ->i_mutex > held. Which means ->mmap_sem grabbed while holding ->i_mutex. No > directories involved... Good point, either way it's been fixed. Thanks, Josef ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Possible btrfs deadlock coused by commit 660d3f6c 2012-01-16 22:01 ` Josef Bacik @ 2012-01-16 22:35 ` Chris Samuel 0 siblings, 0 replies; 5+ messages in thread From: Chris Samuel @ 2012-01-16 22:35 UTC (permalink / raw) To: Josef Bacik; +Cc: Al Viro, Stanislaw Gruszka, Patrick, linux-btrfs On 17/01/12 09:01, Josef Bacik wrote: > Good point, either way it's been fixed. Thanks, Is it worth pushing that fix into the stable 3.2.x releases ? cheers, Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2012-01-16 22:35 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-01-16 8:53 Possible btrfs deadlock coused by commit 660d3f6c Stanislaw Gruszka 2012-01-16 14:26 ` Josef Bacik 2012-01-16 20:45 ` Al Viro 2012-01-16 22:01 ` Josef Bacik 2012-01-16 22:35 ` Chris Samuel
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