[PATCH v2 11/14] namei: prepare do_linkat for refactoring

[Dmitry Kadashev <dkadashev@gmail.com>]

This is just a preparation for the move of the main linkat logic to a
separate function to make the logic easier to follow.  This change
contains the flow changes so that the actual change to move the main
logic to a separate function does no change the flow at all.

Changes to the flow here:

1. Flags handling is moved into the retry loop. So it can be moved
into the function with the main logic. The cost here is mainly the
capabilities check on retry, but hopefully that is OK, ESTALE retries
are a slow path anyway.

2. Just like the similar patches for rmdir and others a few commits
before, previously on filename_create() and filename_lookup() error the
function used to exit immediately, and now it will check the return code
to see if ESTALE retry is appropriate. Both filename_create() and
filename_lookup() do their own retries on ESTALE (at least via
filename_parentat() used inside), but this extra check should be
completely fine. Invalid flags will now hit `if retry_estale()` as well.

3. unlikely() is added around the ESTALE check;

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/CAHk-=wiG+sN+2zSoAOggKCGue2kOJvw3rQySvQXsZstRQFTN+g@mail.gmail.com/
Link https://lore.kernel.org/io-uring/CAHk-=wiE_JVny73KRZ6wuhL_5U0RRSmAw678_Cnkh3OHM8C7Jg@mail.gmail.com/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
---
 fs/namei.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 61cf6bbe1e5c..82cb6421b6df 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4391,6 +4391,7 @@ int do_linkat(int olddfd, struct filename *old, int newdfd,
 	int how = 0;
 	int error;
 
+retry:
 	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) {
 		error = -EINVAL;
 		goto out_putnames;
@@ -4407,7 +4408,7 @@ int do_linkat(int olddfd, struct filename *old, int newdfd,
 
 	if (flags & AT_SYMLINK_FOLLOW)
 		how |= LOOKUP_FOLLOW;
-retry:
+
 	error = __filename_lookup(olddfd, old, how, &old_path, NULL);
 	if (error)
 		goto out_putnames;
@@ -4439,14 +4440,13 @@ int do_linkat(int olddfd, struct filename *old, int newdfd,
 			goto retry;
 		}
 	}
-	if (retry_estale(error, how)) {
-		path_put(&old_path);
-		how |= LOOKUP_REVAL;
-		goto retry;
-	}
 out_putpath:
 	path_put(&old_path);
 out_putnames:
+	if (unlikely(retry_estale(error, how))) {
+		how |= LOOKUP_REVAL;
+		goto retry;
+	}
 	putname(old);
 	putname(new);
 
-- 
2.30.2