From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Bacik Subject: Re: mkfs.btrfs on 24 disks in parallel crashes kernel Date: Mon, 15 Nov 2010 11:48:35 -0500 Message-ID: <20101115164834.GA2597@localhost.localdomain> References: <1289275800.9102.16.camel@localhost> <1289289147.9102.21.camel@localhost> <1289830902.3248.85.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Chris Mason , linux-btrfs@vger.kernel.org, Albert Strasheim To: Ian Kent Return-path: In-Reply-To: <1289830902.3248.85.camel@localhost> List-ID: On Mon, Nov 15, 2010 at 10:21:42PM +0800, Ian Kent wrote: > On Tue, 2010-11-09 at 15:52 +0800, Ian Kent wrote: > > Chris, > > > On Tue, 2010-11-09 at 12:10 +0800, Ian Kent wrote: > > > On Mon, 2010-11-08 at 09:22 +0200, Albert Strasheim wrote: > > > > Hello all > > > > > > > > I did some experiments on Fedora 14 with 2.6.35.6, running mkfs.btrfs > > > > followed by a mount in parallel on 24 disks. > > > > > > > > This seems to crash reliably. > > > > > > > > I reported the bug to Fedora here: > > > > > > > > https://bugzilla.redhat.com/show_bug.cgi?id=650261 > > > > > > > > The bug report has some stacktraces and stuff attached. > > > > > > > > I saw stuff like this: > > > > > > > > [ 203.861368] Btrfs loaded > > > > [ 203.871418] device label myvol-12b0f8ba-e1ef-4d00-aae4-578d59d955e4 > > > > devid 1 transid 7 /dev/sdv > > > > [ 203.981371] device label myvol-fe7fdbcd-8f2f-4b34-aa6b-0d3bb7582ebc > > > > devid 1 transid 7 /dev/sdl > > > > [ 203.990234] BUG: unable to handle kernel NULL pointer dereference > > > > at 0000000000000128 > > > > [ 204.001153] IP: [] btrfs_test_super+0x10/0x26 [btrfs] > > > > [ 204.016840] PGD 0 > > > > [ 204.018696] Oops: 0000 [#1] SMP > > > > [ 204.021264] last sysfs file: > > > > /sys/devices/pci0000:00/0000:00:05.0/0000:0d:00.0/host7/port-7:0/expander-7:0/port-7:0:9/end_device-7:0:9/target7:0:9/7:0:9:0/uevent > > > > [ 204.045966] CPU 0 > > > > [ 204.055933] Modules linked in: btrfs zlib_deflate libcrc32c ipv6 > > > > mlx4_ib ib_mad ib_core mlx4_en igb mlx4_core ses iTCO_wdt ioatdma dca > > > > iTCO_vendor_support i7core_edac edac_core enclosure i2c_i801 i2c_core > > > > microcode joydev serio_raw mptsas mptscsih mptbase scsi_transport_sas > > > > [last unloaded: scsi_wait_scan] > > > > [ 204.100672] > > > > [ 204.103025] Pid: 2166, comm: mount Not tainted > > > > 2.6.35.6-48.fc14.x86_64 #1 ASSY,BLADE,X6270 /SUN BLADE X6270 > > > > SERVER MODULE > > > > [ 204.121895] RIP: 0010:[] [] > > > > btrfs_test_super+0x10/0x26 [btrfs] > > > > [ 204.139279] RSP: 0018:ffff8803768ddcd8 EFLAGS: 00010287 > > > > [ 204.144675] RAX: 0000000000000000 RBX: ffff8803772df800 RCX: ffff8801f7d34480 > > > > [ 204.160885] RDX: 0000000000000120 RSI: ffff8801f7d34480 RDI: ffff8803772df800 > > > > [ 204.179473] RBP: ffff8803768ddcd8 R08: ffff8801f7d344f8 R09: ffff880375c78760 > > > > [ 204.185673] R10: ffff8803768ddb68 R11: ffff8801f7d34480 R12: ffffffffa01f13d0 > > > > [ 204.200174] R13: ffffffffa019a000 R14: ffff8801f7d34480 R15: ffffffffa01f1400 > > > > [ 204.221347] FS: 00007f766050d800(0000) GS:ffff880022200000(0000) > > > > knlGS:0000000000000000 > > > > [ 204.226597] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > > > > [ 204.238144] CR2: 0000000000000128 CR3: 00000001f7504000 CR4: 00000000000006f0 > > > > [ 204.256446] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > > [ 204.263975] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > > > > [ 204.280097] Process mount (pid: 2166, threadinfo ffff8803768dc000, > > > > task ffff880376ab8000) > > > > [ 204.296529] Stack: > > > > [ 204.298975] ffff8803768ddd38 ffffffff81118df6 ffffffffa01f13d0 > > > > 0000000000000000 > > > > [ 204.305955] <0> ffffffff811184a7 0000000000000000 ffff8803768ddd38 > > > > 0000000000000003 > > > > [ 204.320999] <0> ffffffffa01f13d0 0000000000000000 ffff880375c78680 > > > > ffff8801f4f59d00 > > > > [ 204.338658] Call Trace: > > > > [ 204.341138] [] sget+0x54/0x367 > > > > [ 204.355474] [] ? set_anon_super+0x0/0xe7 > > > > [ 204.360487] [] btrfs_get_sb+0x108/0x3eb [btrfs] > > > > [ 204.375799] [] vfs_kern_mount+0xad/0x1ac > > > > [ 204.379952] [] do_kern_mount+0x4d/0xef > > > > [ 204.395757] [] do_mount+0x700/0x75d > > > > [ 204.400676] [] ? strndup_user+0x54/0x85 > > > > [ 204.417219] [] sys_mount+0x88/0xc2 > > > > [ 204.420399] [] system_call_fastpath+0x16/0x1b > > > > [ 204.435716] Code: <48> 8b 80 28 01 00 00 48 39 b0 28 22 00 00 c9 0f > > > > 94 c0 0f b6 c0 c3 > > > > [ 204.447369] RIP [] btrfs_test_super+0x10/0x26 [btrfs] > > > > [ 204.458280] RSP > > > > [ 204.462330] CR2: 0000000000000128 > > > > [ 204.466479] ---[ end trace c8bb842fa664d021 ]--- > > > > [ 204.498273] device label myvol-11d50321-7482-4ee2-8da5-5ee5f623ae17 > > > > devid 1 transid 7 /dev/sdk > > > > > > This looks like a fairly obvious race. > > > How about some comments on the suitability of this totally untested > > > patch? > > > > > > I thought about trying to merge the tests following sget() (those > > > surrounded by the mutex) into btrfs_fill_super() but that seemed a bit > > > too hard. Maybe someone can advise on how that should be done if this > > > approach is not OK. > > > > Hahaha, excuse me, of course this is not ok! > > A function local mutex won't do anything to resolve this. > > > > For the sake of discussion let's just assume that it has been defined as > > a static global in fs/btrfs/super.c instead. > > In investigating the traces here I've discovered a few interesting > things. > > First, most of these traces appear to be from a deadlock between the BKL > and dev->bd_mutex in blkdev_{get,put}. The BKL has been removed from > these functions in 2.6.36 and, hopefully a simple patch will fix the > problem for earlier kernels. Hence not a problem to concern yourself > with. > > The second issue (actually two issues) is with btrfs_get_sb(). First the > one from the trace here which is a use before set (in btrfs_test_super) > of the btrfs tree root. Anything that is to be used in the test function > must be set before returning from sget() as the super block is added to > the file system list of supers at the end of sget() and can be used from > that point onward. I've been looking at the code and have concluded that > trying to move the needed code into a set function, that would be used > instead of set_anon_super(), and passed to sget() is difficult and would > be quite messy. This brings me back to using a static global mutex > around the block of code similar to what I have in the patch I posted > here, which I think should also resolve the problem. > So I think we're on the same page for this problem, I've posted a test patch to the bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=650261 Basically we just need to setup a blank root/fs_info so it can be set in set_super, and then we use those blank structs in open_ctree. Hopefully this works, if it does I'll post it to the list for wider review. > Could you have a look at this area of the code and offer your advice on > how you think it would be best to resolve it please. > > Oh and the second problem I noticed was a possible use after clear of > the tree root. The put_super super block method is call a little before > the super block is removed from the file system list of supers leaving a > very small window for this to be used after it has been cleared. I think > it's easily fixed by adding a check of s->s_active being 0 in > btrfs_test_super(), as that will tell us the super block about to go > away. So, again not something for you to worry about as I'll forward > patches when the above is resolved. > put_super should be called after kill_sb() which is what removes us from the fs_supers list, so we should be ok here. Thanks, Josef