Mark Brown:
> With -next 20110113 I'm experiencing lockups shortly after userspace
> starts when booting with my root filesystem on NFS, log below. I can
> boot into /bin/sh but running real userspace triggers this very easily.
> This was introduced sometime this week.
>
> I've not bisected or otherwise investigated much yet, but I do notice
> code added recently by Nick in "fs: rcu-walk for path lookup" showing up
> in the backtrace so including him in the CCs.
This and a report from Santosh Shilimkar look like the same problem
which I reported, and I am testing this patch. If you can, please try it
too.
Note: Of course this is not offcial fix.
J. R. Okajima
diff --git a/fs/namei.c b/fs/namei.c
index 5bb7588..51d052f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -480,6 +480,7 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
{
struct fs_struct *fs = current->fs;
struct dentry *parent = nd->path.dentry;
+ int isroot;
BUG_ON(!(nd->flags & LOOKUP_RCU));
if (nd->root.mnt) {
@@ -489,18 +490,22 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
goto err_root;
}
spin_lock(&parent->d_lock);
- spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
- if (!__d_rcu_to_refcount(dentry, nd->seq))
- goto err;
+ isroot = IS_ROOT(dentry);
+ if (!isroot) {
+ spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+ if (!__d_rcu_to_refcount(dentry, nd->seq))
+ goto err;
+ }
/*
* If the sequence check on the child dentry passed, then the child has
* not been removed from its parent. This means the parent dentry must
* be valid and able to take a reference at this point.
*/
- BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
+ BUG_ON(!isroot && dentry->d_parent != parent);
BUG_ON(!parent->d_count);
parent->d_count++;
- spin_unlock(&dentry->d_lock);
+ if (!isroot)
+ spin_unlock(&dentry->d_lock);
spin_unlock(&parent->d_lock);
if (nd->root.mnt) {
path_get(&nd->root);
@@ -513,7 +518,8 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry
nd->flags &= ~LOOKUP_RCU;
return 0;
err:
- spin_unlock(&dentry->d_lock);
+ if (!isroot)
+ spin_unlock(&dentry->d_lock);
spin_unlock(&parent->d_lock);
err_root:
if (nd->root.mnt)
--
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