proc: show locks in /proc/pid/fdinfo/X

Let's show locks which are associated with a file descriptor in
its fdinfo file.

Currently we don't have a reliable way to determine who holds a lock.  We
can find some information in /proc/locks, but PID which is reported there
can be wrong.  For example, a process takes a lock, then forks a child and
dies.  In this case /proc/locks contains the parent pid, which can be
reused by another process.

$ cat /proc/locks
...
6: FLOCK  ADVISORY  WRITE 324 00:13:13431 0 EOF
...

$ ps -C rpcbind
  PID TTY          TIME CMD
  332 ?        00:00:00 rpcbind

$ cat /proc/332/fdinfo/4
pos:	0
flags:	0100000
mnt_id:	22
lock:	1: FLOCK  ADVISORY  WRITE 324 00:13:13431 0 EOF

$ ls -l /proc/332/fd/4
lr-x------ 1 root root 64 Mar  5 14:43 /proc/332/fd/4 -> /run/rpcbind.lock

$ ls -l /proc/324/fd/
total 0
lrwx------ 1 root root 64 Feb 27 14:50 0 -> /dev/pts/0
lrwx------ 1 root root 64 Feb 27 14:50 1 -> /dev/pts/0
lrwx------ 1 root root 64 Feb 27 14:49 2 -> /dev/pts/0

You can see that the process with the 324 pid doesn't hold the lock.

This information is required for proper dumping and restoring file
locks.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Acked-by: Jeff Layton <jlayton@poochiereds.net>
Acked-by: "J. Bruce Fields" <bfields@fieldses.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 52b780fb5258..653faabb07f4 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2590,6 +2590,44 @@ static int locks_show(struct seq_file *f, void *v)
         return 0;
 }
 
+static void __show_fd_locks(struct seq_file *f,
+                        struct list_head *head, int *id,
+                        struct file *filp, struct files_struct *files)
+{
+        struct file_lock *fl;
+
+        list_for_each_entry(fl, head, fl_list) {
+
+                if (filp != fl->fl_file)
+                        continue;
+                if (fl->fl_owner != files &&
+                    fl->fl_owner != filp)
+                        continue;
+
+                (*id)++;
+                seq_puts(f, "lock:\t");
+                lock_get_status(f, fl, *id, "");
+        }
+}
+
+void show_fd_locks(struct seq_file *f,
+                  struct file *filp, struct files_struct *files)
+{
+        struct inode *inode = file_inode(filp);
+        struct file_lock_context *ctx;
+        int id = 0;
+
+        ctx = inode->i_flctx;
+        if (!ctx)
+                return;
+
+        spin_lock(&ctx->flc_lock);
+        __show_fd_locks(f, &ctx->flc_flock, &id, filp, files);
+        __show_fd_locks(f, &ctx->flc_posix, &id, filp, files);
+        __show_fd_locks(f, &ctx->flc_lease, &id, filp, files);
+        spin_unlock(&ctx->flc_lock);
+}
+
 static void *locks_start(struct seq_file *f, loff_t *pos)
         __acquires(&blocked_lock_lock)
 {