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VFS: Add LOOKUP_SHARED flag.

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Some ->lookup handlers will need to drop and retake the parent lock, so
they can safely use d_alloc_parallel().

->lookup can be called with the parent lock either exclusive or shared.

A new flag, LOOKUP_SHARED, tells ->lookup how the parent is locked.

This is rather ugly, but will be gone soon after we move
d_alloc_parallel() out of the directory lock as ->lookup() will *always*
called with a shared lock on the parent.

Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20260904215142.1060510-6-neilb@ownmail.net
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
NeilBrown 2026-09-05 07:48:14 +10:00 committed by Christian Brauner
parent 33d76519f0
commit cc47a1ba19
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2 changed files with 13 additions and 10 deletions
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20
fs/namei.c
View File

@ -1933,7 +1933,7 @@ static noinline struct dentry *lookup_slow(const struct qstr *name,
struct inode *inode = dir->d_inode;
struct dentry *res;
inode_lock_shared(inode);
res = __lookup_slow(name, dir, flags);
res = __lookup_slow(name, dir, flags | LOOKUP_SHARED);
inode_unlock_shared(inode);
return res;
}
@ -1947,7 +1947,7 @@ static struct dentry *lookup_slow_killable(const struct qstr *name,
if (inode_lock_shared_killable(inode))
return ERR_PTR(-EINTR);
res = __lookup_slow(name, dir, flags);
res = __lookup_slow(name, dir, flags | LOOKUP_SHARED);
inode_unlock_shared(inode);
return res;
}
@ -4440,12 +4440,14 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
int error, create_error;
umode_t mode;
bool got_write;
unsigned int shared_flag;
retry:
open_flag = op->open_flag;
got_write = false;
mode = op->mode;
create_error = 0;
shared_flag = (open_flag & O_CREAT) ? 0 : LOOKUP_SHARED;
if (open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
got_write = !mnt_want_write(nd->path.mnt);
@ -4454,10 +4456,10 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
* a different error; we'll be dropping this one anyway.
*/
}
if (open_flag & O_CREAT)
inode_lock(dir_inode);
else
if (shared_flag)
inode_lock_shared(dir_inode);
else
inode_lock(dir_inode);
if (unlikely(IS_DEADDIR(dir_inode))) {
dentry = ERR_PTR(-ENOENT);
@ -4526,7 +4528,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
if (d_in_lookup(dentry)) {
struct dentry *res = dir_inode->i_op->lookup(dir_inode, dentry,
nd->flags);
nd->flags | shared_flag);
d_lookup_done(dentry);
if (unlikely(res)) {
if (IS_ERR(res)) {
@ -4574,10 +4576,10 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
if (file->f_mode & FMODE_OPENED)
fsnotify_open(file);
}
if ((open_flag & O_CREAT) || create_error)
inode_unlock(dir_inode);
else
if (shared_flag)
inode_unlock_shared(dir_inode);
else
inode_unlock(dir_inode);
if (got_write)
mnt_drop_write(nd->path.mnt);

3
include/linux/namei.h
View File

@ -32,8 +32,9 @@ enum { MAX_NESTED_LINKS = 8 };
#define LOOKUP_CREATE BIT(17) /* ... in object creation */
#define LOOKUP_EXCL BIT(18) /* ... in target must not exist */
#define LOOKUP_RENAME_TARGET BIT(19) /* ... in destination of rename() */
#define LOOKUP_SHARED BIT(20) /* Parent lock is held shared */
/* 4 spare bits for intent */
/* 3 spare bits for intent */
/* Scoping flags for lookup. */
#define LOOKUP_NO_SYMLINKS BIT(24) /* No symlink crossing. */