From e509d6e9c1ab54af257d4ed95b30d41e3d786857 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 17 Sep 2019 22:16:58 -0400
Subject: [PATCH 1/4] autofs_clear_leaf_automount_flags(): use ino->count
instead of ->d_subdirs
We want to find out if the parent will become empty after we remove
the victim of rmdir(). Checking if the victim is the only element
of parent's ->d_subdirs is completely wrong - e.g. opening the parent
will end up with a cursor added to its ->d_parent and fooling the
check.
We do maintain ino->count - 0 for anything removed, 1 + number of
children for anything live. Which gives us precisely what we need
for that check...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/autofs/root.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 29abafc0ce31..2065281ee8b1 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -660,7 +660,6 @@ static void autofs_set_leaf_automount_flags(struct dentry *dentry)
static void autofs_clear_leaf_automount_flags(struct dentry *dentry)
{
- struct list_head *d_child;
struct dentry *parent;
/* flags for dentrys in the root are handled elsewhere */
@@ -673,10 +672,7 @@ static void autofs_clear_leaf_automount_flags(struct dentry *dentry)
/* only consider parents below dentrys in the root */
if (IS_ROOT(parent->d_parent))
return;
- d_child = &dentry->d_child;
- /* Set parent managed if it's becoming empty */
- if (d_child->next == &parent->d_subdirs &&
- d_child->prev == &parent->d_subdirs)
+ if (atomic_read(&autofs_dentry_ino(parent)->count) == 2)
managed_dentry_set_managed(parent);
}
From 41ca19740a0e772eff1f9ba67293649feb836662 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 17 Sep 2019 23:23:08 -0400
Subject: [PATCH 2/4] autofs: get rid of pointless checks around ->count
handling
* IS_ROOT can't be true for unlink or rmdir victim
* any positive autofs dentry has non-NULL autofs_dentry_ino()
* autofs symlink can't have ->count other than 1
* autofs empty directory can't have ->count other than 1
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/autofs/root.c | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 2065281ee8b1..7806b110e79d 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -571,8 +571,7 @@ static int autofs_dir_symlink(struct inode *dir,
dget(dentry);
atomic_inc(&ino->count);
p_ino = autofs_dentry_ino(dentry->d_parent);
- if (p_ino && !IS_ROOT(dentry))
- atomic_inc(&p_ino->count);
+ atomic_inc(&p_ino->count);
dir->i_mtime = current_time(dir);
@@ -610,11 +609,9 @@ static int autofs_dir_unlink(struct inode *dir, struct dentry *dentry)
if (sbi->flags & AUTOFS_SBI_CATATONIC)
return -EACCES;
- if (atomic_dec_and_test(&ino->count)) {
- p_ino = autofs_dentry_ino(dentry->d_parent);
- if (p_ino && !IS_ROOT(dentry))
- atomic_dec(&p_ino->count);
- }
+ atomic_dec(&ino->count);
+ p_ino = autofs_dentry_ino(dentry->d_parent);
+ atomic_dec(&p_ino->count);
dput(ino->dentry);
d_inode(dentry)->i_size = 0;
@@ -706,11 +703,9 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
if (sbi->version < 5)
autofs_clear_leaf_automount_flags(dentry);
- if (atomic_dec_and_test(&ino->count)) {
- p_ino = autofs_dentry_ino(dentry->d_parent);
- if (p_ino && dentry->d_parent != dentry)
- atomic_dec(&p_ino->count);
- }
+ atomic_dec(&ino->count);
+ p_ino = autofs_dentry_ino(dentry->d_parent);
+ atomic_dec(&p_ino->count);
dput(ino->dentry);
d_inode(dentry)->i_size = 0;
clear_nlink(d_inode(dentry));
@@ -758,8 +753,7 @@ static int autofs_dir_mkdir(struct inode *dir,
dget(dentry);
atomic_inc(&ino->count);
p_ino = autofs_dentry_ino(dentry->d_parent);
- if (p_ino && !IS_ROOT(dentry))
- atomic_inc(&p_ino->count);
+ atomic_inc(&p_ino->count);
inc_nlink(dir);
dir->i_mtime = current_time(dir);
From c3aed16680cd0c0e5abf1bfc0dc1338e6a41b29f Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 17 Sep 2019 23:28:08 -0400
Subject: [PATCH 3/4] autofs_dir_rmdir(): check ino->count for deciding whether
it's empty...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/autofs/root.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 7806b110e79d..ae1d112b6f64 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -691,11 +691,10 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
if (sbi->flags & AUTOFS_SBI_CATATONIC)
return -EACCES;
- spin_lock(&sbi->lookup_lock);
- if (!simple_empty(dentry)) {
- spin_unlock(&sbi->lookup_lock);
+ if (atomic_read(&ino->count) != 1)
return -ENOTEMPTY;
- }
+
+ spin_lock(&sbi->lookup_lock);
__autofs_add_expiring(dentry);
d_drop(dentry);
spin_unlock(&sbi->lookup_lock);
From 850d71acd52cd331474116fbd60cf8b3f3ded93e Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 17 Sep 2019 23:31:27 -0400
Subject: [PATCH 4/4] autofs: don't bother with atomics for ino->count
All writers are serialized on inode->i_rwsem. So are the readers
outside of expire.c. And the readers in expire.c are in the
code that really doesn't care about narrow races - it's looking
for expiry candidates and its callers have to cope with the
possibility of a good candidate becoming busy right under them.
No point bothering with atomic operations - just use int and
mark the non-serialized readers with READ_ONCE().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/autofs/autofs_i.h | 2 +-
fs/autofs/expire.c | 6 +++---
fs/autofs/root.c | 20 ++++++++++----------
3 files changed, 14 insertions(+), 14 deletions(-)
diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
index 8bcec8dcabb6..054f97b07754 100644
--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -63,7 +63,7 @@ struct autofs_info {
struct autofs_sb_info *sbi;
unsigned long last_used;
- atomic_t count;
+ int count;
kuid_t uid;
kgid_t gid;
diff --git a/fs/autofs/expire.c b/fs/autofs/expire.c
index 2866fabf497f..31d616aa6fc9 100644
--- a/fs/autofs/expire.c
+++ b/fs/autofs/expire.c
@@ -211,7 +211,7 @@ static int autofs_tree_busy(struct vfsmount *mnt,
}
} else {
struct autofs_info *ino = autofs_dentry_ino(p);
- unsigned int ino_count = atomic_read(&ino->count);
+ unsigned int ino_count = READ_ONCE(ino->count);
/* allow for dget above and top is already dgot */
if (p == top)
@@ -379,7 +379,7 @@ static struct dentry *should_expire(struct dentry *dentry,
/* Not a forced expire? */
if (!(how & AUTOFS_EXP_FORCED)) {
/* ref-walk currently on this dentry? */
- ino_count = atomic_read(&ino->count) + 1;
+ ino_count = READ_ONCE(ino->count) + 1;
if (d_count(dentry) > ino_count)
return NULL;
}
@@ -396,7 +396,7 @@ static struct dentry *should_expire(struct dentry *dentry,
/* Not a forced expire? */
if (!(how & AUTOFS_EXP_FORCED)) {
/* ref-walk currently on this dentry? */
- ino_count = atomic_read(&ino->count) + 1;
+ ino_count = READ_ONCE(ino->count) + 1;
if (d_count(dentry) > ino_count)
return NULL;
}
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index ae1d112b6f64..5aaa1732bf1e 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -569,9 +569,9 @@ static int autofs_dir_symlink(struct inode *dir,
d_add(dentry, inode);
dget(dentry);
- atomic_inc(&ino->count);
+ ino->count++;
p_ino = autofs_dentry_ino(dentry->d_parent);
- atomic_inc(&p_ino->count);
+ p_ino->count++;
dir->i_mtime = current_time(dir);
@@ -609,9 +609,9 @@ static int autofs_dir_unlink(struct inode *dir, struct dentry *dentry)
if (sbi->flags & AUTOFS_SBI_CATATONIC)
return -EACCES;
- atomic_dec(&ino->count);
+ ino->count--;
p_ino = autofs_dentry_ino(dentry->d_parent);
- atomic_dec(&p_ino->count);
+ p_ino->count--;
dput(ino->dentry);
d_inode(dentry)->i_size = 0;
@@ -669,7 +669,7 @@ static void autofs_clear_leaf_automount_flags(struct dentry *dentry)
/* only consider parents below dentrys in the root */
if (IS_ROOT(parent->d_parent))
return;
- if (atomic_read(&autofs_dentry_ino(parent)->count) == 2)
+ if (autofs_dentry_ino(parent)->count == 2)
managed_dentry_set_managed(parent);
}
@@ -691,7 +691,7 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
if (sbi->flags & AUTOFS_SBI_CATATONIC)
return -EACCES;
- if (atomic_read(&ino->count) != 1)
+ if (ino->count != 1)
return -ENOTEMPTY;
spin_lock(&sbi->lookup_lock);
@@ -702,9 +702,9 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
if (sbi->version < 5)
autofs_clear_leaf_automount_flags(dentry);
- atomic_dec(&ino->count);
+ ino->count--;
p_ino = autofs_dentry_ino(dentry->d_parent);
- atomic_dec(&p_ino->count);
+ p_ino->count--;
dput(ino->dentry);
d_inode(dentry)->i_size = 0;
clear_nlink(d_inode(dentry));
@@ -750,9 +750,9 @@ static int autofs_dir_mkdir(struct inode *dir,
autofs_set_leaf_automount_flags(dentry);
dget(dentry);
- atomic_inc(&ino->count);
+ ino->count++;
p_ino = autofs_dentry_ino(dentry->d_parent);
- atomic_inc(&p_ino->count);
+ p_ino->count++;
inc_nlink(dir);
dir->i_mtime = current_time(dir);