[06/12] fs/file.c: remove sanity_check and add likely/unlikely in alloc_fd()

Commit Message

Al Viro Aug. 22, 2024, 12:22 a.m. UTC

From: Yu Ma <[e-mail]>

alloc_fd() has a sanity check inside to make sure the struct file mapping to the
allocated fd is NULL. Remove this sanity check since it can be assured by
exisitng zero initilization and NULL set when recycling fd. Meanwhile, add
likely/unlikely and expand_file() call avoidance to reduce the work under
file_lock.

Reviewed-by: Jan Kara <[e-mail]>
Reviewed-by: Tim Chen <[e-mail]>
Signed-off-by: Yu Ma <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>
---
 fs/file.c | 33 ++++++++++++++-------------------
 1 file changed, 14 insertions(+), 19 deletions(-)

Patch

diff --git a/fs/file.c b/fs/file.c
index dcafae2acae8..9b8df3bc6fea 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -496,7 +496,7 @@  static int alloc_fd(unsigned start, unsigned end, unsigned flags)
 	if (fd < files->next_fd)
 		fd = files->next_fd;
 
-	if (fd < fdt->max_fds)
+	if (likely(fd < fdt->max_fds))
 		fd = find_next_fd(fdt, fd);
 
 	/*
@@ -504,19 +504,21 @@  static int alloc_fd(unsigned start, unsigned end, unsigned flags)
 	 * will limit the total number of files that can be opened.
 	 */
 	error = -EMFILE;
-	if (fd >= end)
+	if (unlikely(fd >= end))
 		goto out;
 
-	error = expand_files(files, fd);
-	if (error < 0)
-		goto out;
+	if (unlikely(fd >= fdt->max_fds)) {
+		error = expand_files(files, fd);
+		if (error < 0)
+			goto out;
 
-	/*
-	 * If we needed to expand the fs array we
-	 * might have blocked - try again.
-	 */
-	if (error)
-		goto repeat;
+		/*
+		 * If we needed to expand the fs array we
+		 * might have blocked - try again.
+		 */
+		if (error)
+			goto repeat;
+	}
 
 	if (start <= files->next_fd)
 		files->next_fd = fd + 1;
@@ -527,13 +529,6 @@  static int alloc_fd(unsigned start, unsigned end, unsigned flags)
 	else
 		__clear_close_on_exec(fd, fdt);
 	error = fd;
-#if 1
-	/* Sanity check */
-	if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
-		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
-		rcu_assign_pointer(fdt->fd[fd], NULL);
-	}
-#endif
 
 out:
 	spin_unlock(&files->file_lock);
@@ -599,7 +594,7 @@  void fd_install(unsigned int fd, struct file *file)
 		rcu_read_unlock_sched();
 		spin_lock(&files->file_lock);
 		fdt = files_fdtable(files);
-		BUG_ON(fdt->fd[fd] != NULL);
+		WARN_ON(fdt->fd[fd] != NULL);
 		rcu_assign_pointer(fdt->fd[fd], file);
 		spin_unlock(&files->file_lock);
 		return;