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authorLinus Torvalds <torvalds@linux-foundation.org>2022-08-03 21:43:12 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-08-03 21:43:12 +0300
commit200e340f2196d7fd427a5810d06e893b932f145a (patch)
tree4456f23530138623ebed57fa2369affabe68368f /fs
parenta782e866497217f22c5d9014cbb7be8549151376 (diff)
parent50417d22d0efbb1be76c3cb66b2329f83741c9c7 (diff)
downloadlinux-200e340f2196d7fd427a5810d06e893b932f145a.tar.xz
Merge tag 'pull-work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs dcache updates from Al Viro: "The main part here is making parallel lookups safe for RT - making sure preemption is disabled in start_dir_add()/ end_dir_add() sections (on non-RT it's automatic, on RT it needs to to be done explicitly) and moving wakeups from __d_lookup_done() inside of such to the end of those sections. Wakeups can be safely delayed for as long as ->d_lock on in-lookup dentry is held; proving that has caught a bug in d_add_ci() that allows memory corruption when sufficiently bogus ntfs (or case-insensitive xfs) image is mounted. Easily fixed, fortunately" * tag 'pull-work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: fs/dcache: Move wakeup out of i_seq_dir write held region. fs/dcache: Move the wakeup from __d_lookup_done() to the caller. fs/dcache: Disable preemption on i_dir_seq write side on PREEMPT_RT d_add_ci(): make sure we don't miss d_lookup_done()
Diffstat (limited to 'fs')
-rw-r--r--fs/dcache.c54
1 files changed, 43 insertions, 11 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index 93f4f5ee07bf..ea5cdec24ea7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2240,6 +2240,7 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
}
res = d_splice_alias(inode, found);
if (res) {
+ d_lookup_done(found);
dput(found);
return res;
}
@@ -2563,7 +2564,15 @@ EXPORT_SYMBOL(d_rehash);
static inline unsigned start_dir_add(struct inode *dir)
{
-
+ /*
+ * The caller holds a spinlock (dentry::d_lock). On !PREEMPT_RT
+ * kernels spin_lock() implicitly disables preemption, but not on
+ * PREEMPT_RT. So for RT it has to be done explicitly to protect
+ * the sequence count write side critical section against a reader
+ * or another writer preempting, which would result in a live lock.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_disable();
for (;;) {
unsigned n = dir->i_dir_seq;
if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
@@ -2572,9 +2581,13 @@ static inline unsigned start_dir_add(struct inode *dir)
}
}
-static inline void end_dir_add(struct inode *dir, unsigned n)
+static inline void end_dir_add(struct inode *dir, unsigned int n,
+ wait_queue_head_t *d_wait)
{
smp_store_release(&dir->i_dir_seq, n + 2);
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ preempt_enable();
+ wake_up_all(d_wait);
}
static void d_wait_lookup(struct dentry *dentry)
@@ -2701,32 +2714,50 @@ mismatch:
}
EXPORT_SYMBOL(d_alloc_parallel);
-void __d_lookup_done(struct dentry *dentry)
+/*
+ * - Unhash the dentry
+ * - Retrieve and clear the waitqueue head in dentry
+ * - Return the waitqueue head
+ */
+static wait_queue_head_t *__d_lookup_unhash(struct dentry *dentry)
{
- struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
- dentry->d_name.hash);
+ wait_queue_head_t *d_wait;
+ struct hlist_bl_head *b;
+
+ lockdep_assert_held(&dentry->d_lock);
+
+ b = in_lookup_hash(dentry->d_parent, dentry->d_name.hash);
hlist_bl_lock(b);
dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
__hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
- wake_up_all(dentry->d_wait);
+ d_wait = dentry->d_wait;
dentry->d_wait = NULL;
hlist_bl_unlock(b);
INIT_HLIST_NODE(&dentry->d_u.d_alias);
INIT_LIST_HEAD(&dentry->d_lru);
+ return d_wait;
+}
+
+void __d_lookup_unhash_wake(struct dentry *dentry)
+{
+ spin_lock(&dentry->d_lock);
+ wake_up_all(__d_lookup_unhash(dentry));
+ spin_unlock(&dentry->d_lock);
}
-EXPORT_SYMBOL(__d_lookup_done);
+EXPORT_SYMBOL(__d_lookup_unhash_wake);
/* inode->i_lock held if inode is non-NULL */
static inline void __d_add(struct dentry *dentry, struct inode *inode)
{
+ wait_queue_head_t *d_wait;
struct inode *dir = NULL;
unsigned n;
spin_lock(&dentry->d_lock);
if (unlikely(d_in_lookup(dentry))) {
dir = dentry->d_parent->d_inode;
n = start_dir_add(dir);
- __d_lookup_done(dentry);
+ d_wait = __d_lookup_unhash(dentry);
}
if (inode) {
unsigned add_flags = d_flags_for_inode(inode);
@@ -2738,7 +2769,7 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode)
}
__d_rehash(dentry);
if (dir)
- end_dir_add(dir, n);
+ end_dir_add(dir, n, d_wait);
spin_unlock(&dentry->d_lock);
if (inode)
spin_unlock(&inode->i_lock);
@@ -2885,6 +2916,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
bool exchange)
{
struct dentry *old_parent, *p;
+ wait_queue_head_t *d_wait;
struct inode *dir = NULL;
unsigned n;
@@ -2915,7 +2947,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
if (unlikely(d_in_lookup(target))) {
dir = target->d_parent->d_inode;
n = start_dir_add(dir);
- __d_lookup_done(target);
+ d_wait = __d_lookup_unhash(target);
}
write_seqcount_begin(&dentry->d_seq);
@@ -2951,7 +2983,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
write_seqcount_end(&dentry->d_seq);
if (dir)
- end_dir_add(dir, n);
+ end_dir_add(dir, n, d_wait);
if (dentry->d_parent != old_parent)
spin_unlock(&dentry->d_parent->d_lock);