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

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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 <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Alexander Viro <[email protected]>
Acked-by: Jeff Layton <[email protected]>
Acked-by: "J. Bruce Fields" <[email protected]>
Acked-by: Cyrill Gorcunov <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Joe Perches <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andrey Vagin 2015-04-16 12:49:38 -07:00 • committed by Linus Torvalds
commit 6c8c90319c
4 changed files with 66 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

27
fs/proc/fd.c
View file

@ -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)