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Subject[PATCH] d_drop should use per dentry lock
d_drop() must use the dentry->d_lock spinlock. In some cases __d_drop() 
was used without holding the dentry->d_lock spinlock, too. This could
end in a race with __d_lookup().

Regards,
Jan

Signed-off-by: Jan Blunck <j.blunck@tu-harburg.de>

fs/autofs4/root.c | 2 ++
fs/dcache.c | 3 +++
fs/namei.c | 14 +++++---------
fs/proc/base.c | 6 +++++-
fs/sysfs/inode.c | 6 +++++-
include/linux/dcache.h | 2 ++
6 files changed, 22 insertions(+), 11 deletions(-)

Index: testing-um/include/linux/dcache.h
===================================================================
--- testing-um.orig/include/linux/dcache.h 2005-01-28 15:06:27.000000000 +0100
+++ testing-um/include/linux/dcache.h 2005-01-28 15:58:15.000000000 +0100
@@ -186,7 +186,9 @@
static inline void d_drop(struct dentry *dentry)
{
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
__d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}

Index: testing-um/fs/namei.c
===================================================================
--- testing-um.orig/fs/namei.c 2005-01-28 15:58:15.000000000 +0100
+++ testing-um/fs/namei.c 2005-01-28 15:58:15.000000000 +0100
@@ -1684,17 +1684,13 @@
void dentry_unhash(struct dentry *dentry)
{
dget(dentry);
- spin_lock(&dcache_lock);
- switch (atomic_read(&dentry->d_count)) {
- default:
- spin_unlock(&dcache_lock);
+ if (atomic_read(&dentry->d_count))
shrink_dcache_parent(dentry);
- spin_lock(&dcache_lock);
- if (atomic_read(&dentry->d_count) != 2)
- break;
- case 2:
+ spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
+ if (atomic_read(&dentry->d_count) == 2)
__d_drop(dentry);
- }
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
}

Index: testing-um/fs/sysfs/inode.c
===================================================================
--- testing-um.orig/fs/sysfs/inode.c 2005-01-28 15:06:24.000000000 +0100
+++ testing-um/fs/sysfs/inode.c 2005-01-28 15:58:15.000000000 +0100
@@ -129,13 +129,17 @@

if (dentry) {
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
if (!(d_unhashed(dentry) && dentry->d_inode)) {
dget_locked(dentry);
__d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
simple_unlink(parent->d_inode, dentry);
- } else
+ } else {
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
+ }
}
}

Index: testing-um/fs/dcache.c
===================================================================
--- testing-um.orig/fs/dcache.c 2005-01-28 15:53:19.000000000 +0100
+++ testing-um/fs/dcache.c 2005-01-28 16:52:49.609883016 +0100
@@ -340,13 +340,16 @@
tmp = head;
while ((tmp = tmp->next) != head) {
struct dentry *dentry = list_entry(tmp, struct dentry, d_alias);
+ spin_lock(&dentry->d_lock);
if (!atomic_read(&dentry->d_count)) {
__dget_locked(dentry);
__d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
dput(dentry);
goto restart;
}
+ spin_unlock(&dentry->d_lock);
}
spin_unlock(&dcache_lock);
}
Index: testing-um/fs/autofs4/root.c
===================================================================
--- testing-um.orig/fs/autofs4/root.c 2005-01-28 15:53:22.000000000 +0100
+++ testing-um/fs/autofs4/root.c 2005-01-28 16:04:35.000000000 +0100
@@ -605,7 +605,9 @@
spin_unlock(&dcache_lock);
return -ENOTEMPTY;
}
+ spin_lock(&dentry->d_lock);
__d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);

dput(ino->dentry);
Index: testing-um/fs/proc/base.c
===================================================================
--- testing-um.orig/fs/proc/base.c 2005-01-28 15:53:38.000000000 +0100
+++ testing-um/fs/proc/base.c 2005-01-28 16:29:14.000000000 +0100
@@ -1468,11 +1468,15 @@
if (proc_dentry != NULL) {

spin_lock(&dcache_lock);
+ spin_lock(&proc_dentry->d_lock);
if (!d_unhashed(proc_dentry)) {
dget_locked(proc_dentry);
__d_drop(proc_dentry);
- } else
+ spin_unlock(&proc_dentry->d_lock);
+ } else {
+ spin_unlock(&proc_dentry->d_lock);
proc_dentry = NULL;
+ }
spin_unlock(&dcache_lock);
}
return proc_dentry;
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