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Message-ID: <20250206054504.2950516-14-neilb@suse.de>
Date: Thu, 6 Feb 2025 16:42:50 +1100
From: NeilBrown <neilb@...e.de>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>,
Jan Kara <jack@...e.cz>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jeff Layton <jlayton@...nel.org>,
Dave Chinner <david@...morbit.com>
Cc: linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 13/19] VFS: lock dentry for ->revalidate to avoid races with rename etc
When we call ->revalidate we want to be sure we are revalidating the
expected name. As a shared lock on i_rwsem no longer prevents renames
we need to lock the dentry and ensure it still has the expected name.
So pass parent name to d_revalidate() and be prepared to retry the
lookup if it returns -EAGAIN.
Signed-off-by: NeilBrown <neilb@...e.de>
---
fs/namei.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 38 insertions(+), 11 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 145ae07f9b8c..3a107d6098be 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -957,12 +957,24 @@ static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry)
}
static inline int d_revalidate(struct inode *dir, const struct qstr *name,
- struct dentry *dentry, unsigned int flags)
+ struct dentry *dentry, unsigned int flags,
+ struct dentry *base, const struct qstr *last)
{
- if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
- return dentry->d_op->d_revalidate(dir, name, dentry, flags);
- else
+ int status;
+
+ if (!unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
return 1;
+
+ if (dentry->d_flags & LOOKUP_RCU) {
+ if (!d_update_trylock(dentry, base, last))
+ return -ECHILD;
+ } else {
+ if (!d_update_lock(dentry, base, last, I_MUTEX_NORMAL))
+ return -EAGAIN;
+ }
+ status = dentry->d_op->d_revalidate(dir, name, dentry, flags);
+ d_update_unlock(dentry);
+ return status;
}
/**
@@ -1686,13 +1698,18 @@ static struct dentry *lookup_dcache(const struct qstr *name,
struct dentry *dir,
unsigned int flags)
{
- struct dentry *dentry = d_lookup(dir, name);
+ struct dentry *dentry;
+again:
+ dentry = d_lookup(dir, name);
if (dentry) {
- int error = d_revalidate(dir->d_inode, name, dentry, flags);
+ int error = d_revalidate(dir->d_inode, name, dentry, flags, dir, name);
if (unlikely(error <= 0)) {
if (!error)
d_invalidate(dentry);
dput(dentry);
+ if (error == -EAGAIN)
+ /* raced with rename etc */
+ goto again;
return ERR_PTR(error);
}
}
@@ -1915,6 +1932,7 @@ static struct dentry *lookup_fast(struct nameidata *nd)
* of a false negative due to a concurrent rename, the caller is
* going to fall back to non-racy lookup.
*/
+again:
if (nd->flags & LOOKUP_RCU) {
dentry = __d_lookup_rcu(parent, &nd->last, &nd->next_seq);
if (unlikely(!dentry)) {
@@ -1930,7 +1948,7 @@ static struct dentry *lookup_fast(struct nameidata *nd)
if (read_seqcount_retry(&parent->d_seq, nd->seq))
return ERR_PTR(-ECHILD);
- status = d_revalidate(nd->inode, &nd->last, dentry, nd->flags);
+ status = d_revalidate(nd->inode, &nd->last, dentry, nd->flags, parent, &nd->last);
if (likely(status > 0))
return dentry;
if (!try_to_unlazy_next(nd, dentry))
@@ -1938,17 +1956,19 @@ static struct dentry *lookup_fast(struct nameidata *nd)
if (status == -ECHILD)
/* we'd been told to redo it in non-rcu mode */
status = d_revalidate(nd->inode, &nd->last,
- dentry, nd->flags);
+ dentry, nd->flags, parent, &nd->last);
} else {
dentry = __d_lookup(parent, &nd->last);
if (unlikely(!dentry))
return NULL;
- status = d_revalidate(nd->inode, &nd->last, dentry, nd->flags);
+ status = d_revalidate(nd->inode, &nd->last, dentry, nd->flags, parent, &nd->last);
}
if (unlikely(status <= 0)) {
if (!status)
d_invalidate(dentry);
dput(dentry);
+ if (status == -EAGAIN)
+ goto again;
return ERR_PTR(status);
}
return dentry;
@@ -1970,7 +1990,7 @@ static struct dentry *__lookup_slow(const struct qstr *name,
if (IS_ERR(dentry))
return dentry;
if (unlikely(!d_in_lookup(dentry))) {
- int error = d_revalidate(inode, name, dentry, flags);
+ int error = d_revalidate(inode, name, dentry, flags, dir, name);
if (unlikely(error <= 0)) {
if (!error) {
d_invalidate(dentry);
@@ -1978,6 +1998,8 @@ static struct dentry *__lookup_slow(const struct qstr *name,
goto again;
}
dput(dentry);
+ if (error == -EAGAIN)
+ goto again;
dentry = ERR_PTR(error);
}
} else {
@@ -3777,6 +3799,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
return ERR_PTR(-ENOENT);
file->f_mode &= ~FMODE_CREATED;
+again:
dentry = d_lookup(dir, &nd->last);
for (;;) {
if (!dentry) {
@@ -3787,9 +3810,13 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
if (d_in_lookup(dentry))
break;
- error = d_revalidate(dir_inode, &nd->last, dentry, nd->flags);
+ error = d_revalidate(dir_inode, &nd->last, dentry, nd->flags, dir, &nd->last);
if (likely(error > 0))
break;
+ if (error == -EAGAIN) {
+ dput(dentry);
+ goto again;
+ }
if (error)
goto out_dput;
d_invalidate(dentry);
--
2.47.1
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