lookup_one_qstr_excl() is used for lookups prior to directory
modifications, whether create, unlink, rename, or whatever.
To prepare for allowing modification to happen in parallel, change
lookup_one_qstr_excl() to use d_alloc_parallel() and change its name to
remove the _excl requirement.
If LOOKUP_EXCL or LOOKUP_RENAME_TARGET is passed, the caller must ensure
d_lookup_done() is called at an appropriate time, and must not assume
that it can test for positive or negative dentries without confirming
that the dentry is no longer d_in_lookup() - unless it is filesystem
code acting one itself and *knows* that ->lookup() always completes the
lookup (currently true for all filesystems other than NFS).
Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
Documentation/filesystems/porting.rst | 11 +++++
fs/namei.c | 58 ++++++++++++++++++---------
2 files changed, 51 insertions(+), 18 deletions(-)
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 385ca21e230e..1feeac9e1483 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -1271,3 +1271,14 @@ completed - typically when it completes with failure.
d_alloc_parallel() no longer requires a waitqueue_head. It used one
from an internal table when needed.
+
+---
+
+** mandatory**
+
+All lookup_and_lock* functions may return a d_in_lookup() dentry if
+passed "O_CREATE|O_EXCL" or "O_RENAME_TARGET". dentry_unlock() calls
+the necessary d_lookup_done(). If the caller *knows* which filesystem
+is being used, it may know that this is not possible. Otherwise it must
+be careful testing if the dentry is positive or negative as the lookup
+may not have been performed yet.
diff --git a/fs/namei.c b/fs/namei.c
index 0703568339d3..e1749fb03cb5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1666,17 +1666,18 @@ static struct dentry *lookup_dcache(const struct qstr *name,
}
/*
- * Parent directory has inode locked exclusive. This is one
- * and only case when ->lookup() gets called on non in-lookup
- * dentries - as the matter of fact, this only gets called
- * when directory is guaranteed to have no in-lookup children
- * at all.
+ * Parent directory has inode locked.
+ * d_lookup_done() must be called before the dentry is dput()
+ * if LOOKUP_EXCL or LOOKUP_RENAME_TARGET is set.
+ * If the dentry is not d_in_lookup():
* Will return -ENOENT if name isn't found and LOOKUP_CREATE wasn't passed.
* Will return -EEXIST if name is found and LOOKUP_EXCL was passed.
+ * If it is d_in_lookup() then these conditions will be checked when
+ * the attempt make to create the act on the name.
*/
-static struct dentry *lookup_one_qstr_excl(const struct qstr *name,
- struct dentry *base,
- unsigned int flags)
+static struct dentry *lookup_one_qstr(const struct qstr *name,
+ struct dentry *base,
+ unsigned int flags)
{
struct dentry *dentry;
struct dentry *old;
@@ -1691,18 +1692,27 @@ static struct dentry *lookup_one_qstr_excl(const struct qstr *name,
if (unlikely(IS_DEADDIR(dir)))
return ERR_PTR(-ENOENT);
- dentry = d_alloc(base, name);
- if (unlikely(!dentry))
- return ERR_PTR(-ENOMEM);
+ dentry = d_alloc_parallel(base, name);
+ if (unlikely(IS_ERR(dentry)))
+ return dentry;
+ if (unlikely(!d_in_lookup(dentry)))
+ /* Raced with another thread which did the lookup */
+ goto found;
old = dir->i_op->lookup(dir, dentry, flags);
if (unlikely(old)) {
+ d_lookup_done(dentry);
dput(dentry);
dentry = old;
}
found:
if (IS_ERR(dentry))
return dentry;
+ if (d_in_lookup(dentry))
+ /* We cannot check for errors - the caller will have to
+ * wait for any create-etc attempt to get relevant errors.
+ */
+ return dentry;
if (d_is_negative(dentry) && !(flags & LOOKUP_CREATE)) {
dput(dentry);
return ERR_PTR(-ENOENT);
@@ -1725,7 +1735,10 @@ static struct dentry *lookup_one_qstr_excl(const struct qstr *name,
* The "necessary locks" are currently the inode node lock on @base.
* The name @last is expected to already have the hash calculated.
* No permission checks are performed.
+ *
* Returns: the dentry, suitably locked, or an ERR_PTR().
+ * The dentry may be d_in_lookup() if LOOKUP_EXCL or LOOKUP_RENAME_TARGET
+ * is given, depending on the filesystem.
*/
struct dentry *lookup_and_lock_hashed(struct qstr *last,
struct dentry *base,
@@ -1735,7 +1748,7 @@ struct dentry *lookup_and_lock_hashed(struct qstr *last,
inode_lock_nested(base->d_inode, I_MUTEX_PARENT);
- dentry = lookup_one_qstr_excl(last, base, lookup_flags);
+ dentry = lookup_one_qstr(last, base, lookup_flags);
if (IS_ERR(dentry))
inode_unlock(base->d_inode);
return dentry;
@@ -1755,7 +1768,7 @@ struct dentry *lookup_and_lock_noperm_locked(struct qstr *last,
if (err < 0)
return ERR_PTR(err);
- return lookup_one_qstr_excl(last, base, lookup_flags);
+ return lookup_one_qstr(last, base, lookup_flags);
}
EXPORT_SYMBOL(lookup_and_lock_noperm_locked);
@@ -1770,7 +1783,10 @@ EXPORT_SYMBOL(lookup_and_lock_noperm_locked);
* The "necessary locks" are currently the inode node lock on @base.
* The name @last is NOT expected to have the hash calculated.
* No permission checks are performed.
+ *
* Returns: the dentry, suitably locked, or an ERR_PTR().
+ * The dentry may be d_in_lookup() if LOOKUP_EXCL or LOOKUP_RENAME_TARGET
+ * is given, depending on the filesystem.
*/
struct dentry *lookup_and_lock_noperm(struct qstr *last,
struct dentry *base,
@@ -1798,7 +1814,10 @@ EXPORT_SYMBOL(lookup_and_lock_noperm);
* The "necessary locks" are currently the inode node lock on @base.
* The name @last is NOT expected to already have the hash calculated.
* Permission checks are performed to ensure %MAY_EXEC access to @base.
+ *
* Returns: the dentry, suitably locked, or an ERR_PTR().
+ * The dentry may be d_in_lookup() if LOOKUP_EXCL or LOOKUP_RENAME_TARGET
+ * is given, depending on the filesystem.
*/
struct dentry *lookup_and_lock(struct mnt_idmap *idmap,
struct qstr *last,
@@ -1826,7 +1845,10 @@ EXPORT_SYMBOL(lookup_and_lock);
* If a fatal signal arrives or is already pending the operation is aborted.
* The name @last is NOT expected to already have the hash calculated.
* Permission checks are performed to ensure %MAY_EXEC access to @base.
+ *
* Returns: the dentry, suitably locked, or an ERR_PTR().
+ * The dentry may be d_in_lookup() if LOOKUP_EXCL or LOOKUP_RENAME_TARGET
+ * is given, depending on the filesystem.
*/
struct dentry *lookup_and_lock_killable(struct mnt_idmap *idmap,
struct qstr *last,
@@ -1843,7 +1865,7 @@ struct dentry *lookup_and_lock_killable(struct mnt_idmap *idmap,
if (err < 0)
return ERR_PTR(err);
- dentry = lookup_one_qstr_excl(last, base, lookup_flags);
+ dentry = lookup_one_qstr(last, base, lookup_flags);
if (IS_ERR(dentry))
inode_unlock(base->d_inode);
return dentry;
@@ -1894,6 +1916,7 @@ EXPORT_SYMBOL(dentry_unlock_dir_locked);
void dentry_unlock(struct dentry *dentry)
{
if (!IS_ERR(dentry)) {
+ d_lookup_done(dentry);
inode_unlock(dentry->d_parent->d_inode);
dentry_unlock_dir_locked(dentry);
}
@@ -3500,8 +3523,7 @@ lookup_and_lock_rename_hashed(struct renamedata *rd, int lookup_flags)
p = lock_rename(rd->old_dir, rd->new_dir);
dget(rd->old_dir);
- d1 = lookup_one_qstr_excl(&rd->old_last, rd->old_dir,
- lookup_flags);
+ d1 = lookup_one_qstr(&rd->old_last, rd->old_dir, lookup_flags);
if (IS_ERR(d1))
goto out_unlock_1;
}
@@ -3513,8 +3535,8 @@ lookup_and_lock_rename_hashed(struct renamedata *rd, int lookup_flags)
}
d2 = dget(rd->new_dentry);
} else {
- d2 = lookup_one_qstr_excl(&rd->new_last, rd->new_dir,
- lookup_flags | target_flags);
+ d2 = lookup_one_qstr(&rd->new_last, rd->new_dir,
+ lookup_flags | target_flags);
if (IS_ERR(d2))
goto out_unlock_2;
}
--
2.49.0
