fs: Split fcntl_rw_hint()

Split fcntl_rw_hint() such that there is one helper function per fcntl.
Use READ_ONCE() and WRITE_ONCE() to access the i_write_hint member
instead of protecting such accesses with the inode lock. READ_ONCE() is
not used in I/O path code that reads i_write_hint. Users who want
F_SET_RW_HINT to affect I/O need to make sure that F_SET_RW_HINT has
completed before I/O is submitted that should use the configured write
hint.

Cc: Christoph Hellwig <hch@lst.de>
Suggested-by: Christoph Hellwig <hch@lst.de>
Cc: Kanchan Joshi <joshi.k@samsung.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240202203926.2478590-4-bvanassche@acm.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index f3bc4662455fe3306e9a60058e20498ebffd34d1..d2b15351ab8e6562783d52eda871bb94a7d5f3dd 100644 (file)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -290,32 +290,33 @@ static bool rw_hint_valid(u64 hint)
        }
 }
 
-static long fcntl_rw_hint(struct file *file, unsigned int cmd,
-                         unsigned long arg)
+static long fcntl_get_rw_hint(struct file *file, unsigned int cmd,
+                             unsigned long arg)
 {
        struct inode *inode = file_inode(file);
        u64 __user *argp = (u64 __user *)arg;
-       u64 hint;
+       u64 hint = READ_ONCE(inode->i_write_hint);
 
-       switch (cmd) {
-       case F_GET_RW_HINT:
-               hint = inode->i_write_hint;
-               if (copy_to_user(argp, &hint, sizeof(*argp)))
-                       return -EFAULT;
-               return 0;
-       case F_SET_RW_HINT:
-               if (copy_from_user(&hint, argp, sizeof(hint)))
-                       return -EFAULT;
-               if (!rw_hint_valid(hint))
-                       return -EINVAL;
+       if (copy_to_user(argp, &hint, sizeof(*argp)))
+               return -EFAULT;
+       return 0;
+}
 
-               inode_lock(inode);
-               inode->i_write_hint = hint;
-               inode_unlock(inode);
-               return 0;
-       default:
+static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
+                             unsigned long arg)
+{
+       struct inode *inode = file_inode(file);
+       u64 __user *argp = (u64 __user *)arg;
+       u64 hint;
+
+       if (copy_from_user(&hint, argp, sizeof(hint)))
+               return -EFAULT;
+       if (!rw_hint_valid(hint))
                return -EINVAL;
-       }
+
+       WRITE_ONCE(inode->i_write_hint, hint);
+
+       return 0;
 }
 
 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
@@ -421,8 +422,10 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
                err = memfd_fcntl(filp, cmd, argi);
                break;
        case F_GET_RW_HINT:
+               err = fcntl_get_rw_hint(filp, cmd, arg);
+               break;
        case F_SET_RW_HINT:
-               err = fcntl_rw_hint(filp, cmd, arg);
+               err = fcntl_set_rw_hint(filp, cmd, arg);
                break;
        default:
                break;