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SubjectRe: 3.7.10+: BUG Dentry still in use [unmount of cifs cifs]
On Tue, 5 Mar 2013 14:08:49 -0500
Jeff Layton <jlayton@redhat.com> wrote:

> On Tue, 05 Mar 2013 10:54:56 -0800
> Ben Greear <greearb@candelatech.com> wrote:
>
> > In doing some CIFS testing (utilizing it's feature to bind to local
> > address..but not sure that matters), we saw this error when trying
> > to un-mount.
> >
> > Our kernel is patched (nfs, some networking related patches), but there
> > are no out-of-kernel patches to CIFS, so I don't *think* this is anything
> > we could have caused.
> >
> > This problem appears to be easily reproducible, so we will be happy
> > to test patches if anyone has any suggestions.
> >
> > BUG: Dentry ffff8800c07e43c0{i=45762,n=cifs2-01.7.lf-data} still in use (1) [unmount of cifs cifs]
> > ------------[ cut here ]------------
> > kernel BUG at /home/greearb/git/linux-3.7.dev.y/fs/dcache.c:967!
> > invalid opcode: 0000 [#1] PREEMPT SMP
> > Modules linked in: nls_utf8 cifs 8021q garp stp llc iptable_raw xt_CT veth nf_nat_ipv4 nf_nat fuse macvlan wanlink(O) pktgen nfsv3 nfs_acl nfsv4 auth_rpcgss nfs
> > fscache lockd sunrpc be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_mad ib_core
> > w83793 iscsi_tcp w83627hf libiscsi_tcp hwmon_vid libiscsi scsi_transport_iscsi coretemp mperf kvm_intel kvm i5k_amb uinput i5000_edac gpio_ich edac_core
> > iTCO_wdt e1000e iTCO_vendor_support lpc_ich i2c_i801 pcspkr ioatdma dca microcode shpchp ipv6 floppy radeon i2c_algo_bit hwmon drm_kms_helper ttm drm i2c_core
> > [last unloaded: iptable_nat]
> > CPU 6
> > Pid: 6610, comm: umount Tainted: G C O 3.7.10+ #74 Supermicro X7DBU/X7DBU
> > RIP: 0010:[<ffffffff811591c9>] [<ffffffff811591c9>] shrink_dcache_for_umount_subtree+0x84/0x194
> > RSP: 0018:ffff8800c0085dc8 EFLAGS: 00010296
> > RAX: 0000000000000062 RBX: ffff8800c07e43c0 RCX: 0000000000000059
> > RDX: ffffffff81bc25a8 RSI: 0000000000000046 RDI: 0000000000000246
> > RBP: ffff8800c0085de8 R08: 0000000000000001 R09: ffff8800c0085cc8
> > R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800c050e9c0
> > R13: ffff880128ee8000 R14: 0000000000000000 R15: ffff8800c0085f28
> > FS: 00007f6084847840(0000) GS:ffff88012fd80000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > CR2: 00007f608442c3a0 CR3: 00000000c7c2d000 CR4: 00000000000007e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > Process umount (pid: 6610, threadinfo ffff8800c0084000, task ffff88012a6a0000)
> > Stack:
> > ffff880128ee8310 00000000000128c0 ffff880128ee8000 ffffffffa06b96b0
> > ffff8800c0085e08 ffffffff81159310 ffff8800c0084000 ffff880128ee8000
> > ffff8800c0085e38 ffffffff81149afe ffff8800c0085e38 0000000000000021
> > Call Trace:
> > [<ffffffff81159310>] shrink_dcache_for_umount+0x37/0x49
> > [<ffffffff81149afe>] generic_shutdown_super+0x20/0xd2
> > [<ffffffff81149c25>] kill_anon_super+0x11/0x1c
> > [<ffffffffa068b1ea>] cifs_kill_sb+0x15/0x21 [cifs]
> > [<ffffffff81149e48>] deactivate_locked_super+0x32/0x5e
> > [<ffffffff8114a942>] deactivate_super+0x40/0x46
> > [<ffffffff8115fdb3>] mntput_no_expire+0x12d/0x136
> > [<ffffffff81160b59>] sys_umount+0x321/0x34c
> > [<ffffffff8114f846>] ? path_put+0x1d/0x21
> > [<ffffffff81525229>] system_call_fastpath+0x16/0x1b
> > Code: 50 28 4c 8b 0a 31 d2 48 85 f6 74 04 48 8b 56 40 48 05 10 03 00 00 48 89 de 48 c7 c7 9d d0 7b 81 48 89 04 24 31 c0 e8 b9 4e 3c 00 <0f> 0b eb fe 4c 8b 63 18
> > 4c 39 e3 75 3c 48 8b 93 90 00 00 00 48
> > RIP [<ffffffff811591c9>] shrink_dcache_for_umount_subtree+0x84/0x194
> > RSP <ffff8800c0085dc8>
> > ---[ end trace 9b2978a89532c292 ]---
>
> Hmmm...dentry leak. Are there any jobs queued to the cifsiod workqueue
> when the box oopses?
>

In fact...

It's just a guess, but does this patch help at all? Note that it builds
but is otherwise untested ;). If it works we might want to go with
something a bit less invasive but this may tell us if we're on the
right track.

------------------[snip]------------------

[PATCH] cifs: flush cifsiod workqueue before unmounting

It's possible that we'll end up with some writeback activity going on
while the fs is unmounted. If that happens we'll queue some work to a
workqueue to handle the last bit of cleanup. At that point though,
there's nothing pinning down the superblock, so it's possible to race
with a umount.

There will still be an active cifsFileInfo reference, and that will
hold a reference to a dentry. That, in turn, can cause a "Dentry still
in use" error. Flush the cifsiod workqueue before allowing a umount
to proceed.

Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
fs/cifs/connect.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 991c63c..7840f3f 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3815,6 +3815,7 @@ cifs_umount(struct cifs_sb_info *cifs_sb)
struct tcon_link *tlink;

cancel_delayed_work_sync(&cifs_sb->prune_tlinks);
+ flush_workqueue(cifsiod_wq);

spin_lock(&cifs_sb->tlink_tree_lock);
while ((node = rb_first(root))) {
--
1.7.11.7


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