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fs: touch up predicts in path lookup 

Rationale:
- ND_ROOT_PRESET is only set in a condition already marked unlikely
- LOOKUP_IS_SCOPED already has unlikely on it, but inconsistently
  applied
- set_root() only fails if there is a bug
- most names are not empty (see !*s)
- most of the time path_init() does not encounter LOOKUP_CACHED without
  LOOKUP_RCU
- LOOKUP_IN_ROOT is a rarely seen flag

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20251105150630.756606-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Mateusz Guzik 2025-11-05 16:06:30 +01:00 committed by Christian Brauner
parent 9eda581bfe
commit 030e86dfda
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 9 additions and 9 deletions
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18
fs/namei.c
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@ -990,8 +990,8 @@ static int complete_walk(struct nameidata *nd)
* We don't want to zero nd->root for scoped-lookups or * We don't want to zero nd->root for scoped-lookups or
* externally-managed nd->root. * externally-managed nd->root.
*/ */
if (!(nd->state & ND_ROOT_PRESET)) if (likely(!(nd->state & ND_ROOT_PRESET)))
if (!(nd->flags & LOOKUP_IS_SCOPED)) if (likely(!(nd->flags & LOOKUP_IS_SCOPED)))
nd->root.mnt = NULL; nd->root.mnt = NULL;
nd->flags &= ~LOOKUP_CACHED; nd->flags &= ~LOOKUP_CACHED;
if (!try_to_unlazy(nd)) if (!try_to_unlazy(nd))
@ -1073,7 +1073,7 @@ static int nd_jump_root(struct nameidata *nd)
} }
if (!nd->root.mnt) { if (!nd->root.mnt) {
int error = set_root(nd); int error = set_root(nd);
if (error) if (unlikely(error))
return error; return error;
} }
if (nd->flags & LOOKUP_RCU) { if (nd->flags & LOOKUP_RCU) {
@ -2140,7 +2140,7 @@ static const char *handle_dots(struct nameidata *nd, int type)
if (!nd->root.mnt) { if (!nd->root.mnt) {
error = ERR_PTR(set_root(nd)); error = ERR_PTR(set_root(nd));
if (error) if (unlikely(error))
return error; return error;
} }
if (nd->flags & LOOKUP_RCU) if (nd->flags & LOOKUP_RCU)
@ -2582,10 +2582,10 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
const char *s = nd->pathname; const char *s = nd->pathname;
/* LOOKUP_CACHED requires RCU, ask caller to retry */ /* LOOKUP_CACHED requires RCU, ask caller to retry */
if ((flags & (LOOKUP_RCU | LOOKUP_CACHED)) == LOOKUP_CACHED) if (unlikely((flags & (LOOKUP_RCU | LOOKUP_CACHED)) == LOOKUP_CACHED))
return ERR_PTR(-EAGAIN); return ERR_PTR(-EAGAIN);
if (!*s) if (unlikely(!*s))
flags &= ~LOOKUP_RCU; flags &= ~LOOKUP_RCU;
if (flags & LOOKUP_RCU) if (flags & LOOKUP_RCU)
rcu_read_lock(); rcu_read_lock();
@ -2599,7 +2599,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
nd->r_seq = __read_seqcount_begin(&rename_lock.seqcount); nd->r_seq = __read_seqcount_begin(&rename_lock.seqcount);
smp_rmb(); smp_rmb();
if (nd->state & ND_ROOT_PRESET) { if (unlikely(nd->state & ND_ROOT_PRESET)) {
struct dentry *root = nd->root.dentry; struct dentry *root = nd->root.dentry;
struct inode *inode = root->d_inode; struct inode *inode = root->d_inode;
if (*s && unlikely(!d_can_lookup(root))) if (*s && unlikely(!d_can_lookup(root)))
@ -2618,7 +2618,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
nd->root.mnt = NULL; nd->root.mnt = NULL;
/* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */ /* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */
if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) { if (*s == '/' && likely(!(flags & LOOKUP_IN_ROOT))) {
error = nd_jump_root(nd); error = nd_jump_root(nd);
if (unlikely(error)) if (unlikely(error))
return ERR_PTR(error); return ERR_PTR(error);
@ -2671,7 +2671,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
} }
/* For scoped-lookups we need to set the root to the dirfd as well. */ /* For scoped-lookups we need to set the root to the dirfd as well. */
if (flags & LOOKUP_IS_SCOPED) { if (unlikely(flags & LOOKUP_IS_SCOPED)) {
nd->root = nd->path; nd->root = nd->path;
if (flags & LOOKUP_RCU) { if (flags & LOOKUP_RCU) {
nd->root_seq = nd->seq; nd->root_seq = nd->seq;