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Date: Wed, 28 Apr 2010 23:35:42 -0700
From: john stultz <johnstul@...ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "Luis Claudio R. Goncalves" <lclaudio@...g.org>,
rt-users <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Nick Piggin <npiggin@...e.de>
Subject: Re: 2.6.33.3-rt16: WARNING: at fs/namespace.c:1197
umount_tree+0x127/0x175()
On Tue, 2010-04-27 at 22:53 +0200, Thomas Gleixner wrote:
> On Tue, 27 Apr 2010, Luis Claudio R. Goncalves wrote:
>
> CC'ed John
>
> > Hello!
> >
> > I see this warning during system boot and it hangs while loading X and even
> > though I can change from one VT to another (ctrl+alt+F<num>) no keys
> > pressed seem to have any effect.
> >
> > ------------[ cut here ]------------
> > WARNING: at fs/namespace.c:1197 umount_tree+0x127/0x175()
> > Hardware name: KQ260AA-AC4 a6540br
> > Modules linked in: i915 drm_kms_helper drm video output ipt_MASQUERADE iptable_nat nf_nat bridge stp llc vfat fat sunrpc ipv6 xt_physdev ipt_REJECT xt_tcpudp nf_conntrack_ipv4 nf_defrag_ipv4 xt_state iptable_filter ip_tables x_tables dm_mirror dm_region_hash dm_log dm_multipath scsi_dh dm_mod kvm_intel kvm uinput tuner_simple tuner_types wm8775 tda9887 tda8290 tuner snd_hda_codec_realtek cx25840 snd_hda_intel snd_hda_codec snd_hwdep snd_seq usb_storage snd_seq_device ivtv snd_pcm i2c_algo_bit cx2341x v4l2_common videodev snd_timer firewire_ohci snd firewire_core v4l1_compat v4l2_compat_ioctl32 ir_common ir_core i2c_i801 soundcore crc_itu_t tveeprom i2c_core iTCO_wdt snd_page_alloc sr_mod intel_agp iTCO_vendor_support serio_raw pcspkr sg button r8169 mii cdrom ahci libata sd_mod scsi_mod crc_t10dif ext3 jbd mbcache uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode]
> > Pid: 2267, comm: libvirtd Not tainted 2.6.33.3-rt16 #28
> > Call Trace:
> > [<ffffffff81040e3b>] warn_slowpath_common+0x7c/0x94
> > [<ffffffff81040e67>] warn_slowpath_null+0x14/0x16
> > [<ffffffff81115a7f>] umount_tree+0x127/0x175
> > [<ffffffff81116d1d>] put_mnt_ns+0xc2/0xf0
> > [<ffffffff81061a1d>] free_nsproxy+0x1f/0x86
> > [<ffffffff81061abc>] switch_task_namespaces+0x38/0x3c
> > [<ffffffff81061ad0>] exit_task_namespaces+0x10/0x12
> > [<ffffffff81044ae3>] do_exit+0x595/0x738
> > [<ffffffff81360626>] ? rt_mutex_unlock+0xe/0x10
> > [<ffffffff81360db8>] ? lockdep_sys_exit_thunk+0x35/0x67
> > [<ffffffff81044d10>] do_group_exit+0x8a/0xb9
> > [<ffffffff81044d56>] sys_exit_group+0x17/0x1b
> > [<ffffffff81002d32>] system_call_fastpath+0x16/0x1b
> > ---[ end trace 348d259112b3e793 ]---
> >
> >
> > The warning comes from:
> >
> > WARN_ON(!(p->mnt_flags & MNT_MOUNTED));
Hey Luis,
So Thomas' current tip/rt/2.6.33 should have the fix for the WARN_ON
already included, however there is still the hang your seeing that I've
been hunting down all of yesterday and today.
Basically it was an issue with namespaces. Nick switched the
dentry->d_mounted counter to a flag, and that gives us problems with
namespaces since the dentry might get attached multiple times. This
causes the first namespace release to cause d_mountpoint to fail and the
mounts to be lost. Thus /proc goes away and things don't seem to take
well to that.
Anyway, the patch below seems to fix it for me. If you could give it a
whirl (again, on top of the current tip/rt/2.6.33 tree) and let me know
how it works for you, I'd appreciate it.
Thanks again!
-john
>>From e33602d947bcbfcb9e7043c6d496c595043a5c74 Mon Sep 17 00:00:00 2001
From: John Stultz <johnstul@...ibm.com>
Date: Wed, 28 Apr 2010 23:31:49 -0700
Subject: [PATCH] Fix namespace related hangs
Nick converted the dentry->d_mounted counter to a flag,
however with namespaces, dentries can be mounted multiple times
(and more importantly unmounted multiple times).
If a namespace was created and then released, the
unmount_tree would remove the DCACHE_MOUNTED flag
and that would make d_mountpoint fail, causing the
mounts to be lost.
This patch coverts it back to a counter, and adds some extra
WARN_ONs to make sure things are accounted properly.
Signed-off-by: John Stultz <johnstul@...ibm.com>
---
fs/autofs4/expire.c | 5 +++--
fs/dcache.c | 1 +
fs/libfs.c | 1 +
fs/namespace.c | 5 +++--
include/linux/dcache.h | 3 ++-
5 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index dc629ee..60a7c6c 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -296,7 +296,8 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
if (d_mountpoint(root)) {
ino->flags |= AUTOFS_INF_MOUNTPOINT;
spin_lock(&root->d_lock);
- root->d_flags &= ~DCACHE_MOUNTED;
+ WARN_ON(root->d_mounted == 0);
+ root->d_mounted--;
spin_unlock(&root->d_lock);
}
ino->flags |= AUTOFS_INF_EXPIRING;
@@ -536,7 +537,7 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_MOUNTPOINT) {
spin_lock(&sb->s_root->d_lock);
- sb->s_root->d_flags |= DCACHE_MOUNTED;
+ sb->s_root->d_mounted++;
spin_unlock(&sb->s_root->d_lock);
ino->flags &= ~AUTOFS_INF_MOUNTPOINT;
}
diff --git a/fs/dcache.c b/fs/dcache.c
index c2a4d2e..89b9d1f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1187,6 +1187,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
dentry->d_sb = NULL;
dentry->d_op = NULL;
dentry->d_fsdata = NULL;
+ dentry->d_mounted = 0;
INIT_HLIST_NODE(&dentry->d_hash);
INIT_LIST_HEAD(&dentry->d_lru);
INIT_LIST_HEAD(&dentry->d_subdirs);
diff --git a/fs/libfs.c b/fs/libfs.c
index 48fe7c8..98d2717 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -265,6 +265,7 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name,
d_instantiate(dentry, root);
s->s_root = dentry;
s->s_flags |= MS_ACTIVE;
+ WARN_ON(mnt->mnt_flags & MNT_MOUNTED);
mnt->mnt_flags |= MNT_MOUNTED;
simple_set_mnt(mnt, s);
return 0;
diff --git a/fs/namespace.c b/fs/namespace.c
index 6c115d8..64db957 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -586,7 +586,8 @@ static void dentry_reset_mounted(struct vfsmount *mnt, struct dentry *dentry)
{
if (!__lookup_mnt(mnt, dentry, 0)) {
spin_lock(&dentry->d_lock);
- dentry->d_flags &= ~DCACHE_MOUNTED;
+ WARN_ON(dentry->d_mounted == 0);
+ dentry->d_mounted--;
spin_unlock(&dentry->d_lock);
}
}
@@ -610,7 +611,7 @@ void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
child_mnt->mnt_parent = mntget(mnt);
spin_lock(&dentry->d_lock);
child_mnt->mnt_mountpoint = dget_dlock(dentry);
- dentry->d_flags |= DCACHE_MOUNTED;
+ dentry->d_mounted++;
spin_unlock(&dentry->d_lock);
}
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 39872ea..bc5a5ff 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -99,6 +99,7 @@ struct dentry {
atomic_t d_count;
unsigned int d_flags; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
+ int d_mounted;
seqcount_t d_seq; /* per dentry seqlock */
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
@@ -364,7 +365,7 @@ extern void dput(struct dentry *);
static inline int d_mountpoint(struct dentry *dentry)
{
- return dentry->d_flags & DCACHE_MOUNTED;
+ return dentry->d_mounted;
}
extern struct vfsmount *lookup_mnt(struct path *);
--
1.6.0.4
--
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