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>

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 6d37062..8e36c7e 100644 (file)
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1709,6 +1709,10 @@ A typical output is
        flags:  0100002
        mnt_id: 19
 
+All locks associated with a file descriptor are shown in its fdinfo too.
+
+lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
+
 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
 pair provide additional information particular to the objects they represent.
 

diff --git a/fs/locks.c b/fs/locks.c
index 52b780f..653faab 100644 (file)
--- 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)
 {

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 8e5ad83..af84ad0 100644 (file)
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -8,6 +8,7 @@
 #include <linux/security.h>
 #include <linux/file.h>
 #include <linux/seq_file.h>
+#include <linux/fs.h>
 
 #include <linux/proc_fs.h>
 
@@ -48,17 +49,23 @@ static int seq_show(struct seq_file *m, void *v)
                put_files_struct(files);
        }
 
-       if (!ret) {
-               seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
-                          (long long)file->f_pos, f_flags,
-                          real_mount(file->f_path.mnt)->mnt_id);
-               if (file->f_op->show_fdinfo)
-                       file->f_op->show_fdinfo(m, file);
-               ret = seq_has_overflowed(m);
-               fput(file);
-       }
+       if (ret)
+               return ret;
 
-       return ret;
+       seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
+                  (long long)file->f_pos, f_flags,
+                  real_mount(file->f_path.mnt)->mnt_id);
+
+       show_fd_locks(m, file, files);
+       if (seq_has_overflowed(m))
+               goto out;
+
+       if (file->f_op->show_fdinfo)
+               file->f_op->show_fdinfo(m, file);
+
+out:
+       fput(file);
+       return 0;
 }
 
 static int seq_fdinfo_open(struct inode *inode, struct file *file)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6bf7ab7..c4e9273 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1042,6 +1042,9 @@ extern void lease_get_mtime(struct inode *, struct timespec *time);
 extern int generic_setlease(struct file *, long, struct file_lock **, void **priv);
 extern int vfs_setlease(struct file *, long, struct file_lock **, void **);
 extern int lease_modify(struct file_lock *, int, struct list_head *);
+struct files_struct;
+extern void show_fd_locks(struct seq_file *f,
+                        struct file *filp, struct files_struct *files);
 #else /* !CONFIG_FILE_LOCKING */
 static inline int fcntl_getlk(struct file *file, unsigned int cmd,
                              struct flock __user *user)
@@ -1178,6 +1181,10 @@ static inline int lease_modify(struct file_lock *fl, int arg,
 {
        return -EINVAL;
 }
+
+struct files_struct;
+static inline void show_fd_locks(struct seq_file *f,
+                       struct file *filp, struct files_struct *files) {}
 #endif /* !CONFIG_FILE_LOCKING */