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Subject[PATCH] proc: show locks in /proc/pid/fdinfo/X
Date
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.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jeff Layton <jlayton@poochiereds.net>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
Documentation/filesystems/proc.txt | 4 ++++
fs/locks.c | 38 ++++++++++++++++++++++++++++++++++++++
fs/proc/fd.c | 27 ++++++++++++++++++---------
include/linux/fs.h | 7 +++++++
4 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index a07ba61..6331623 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1704,6 +1704,10 @@ 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 365c82e..815f832 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2592,6 +2592,44 @@ 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..f04e13d 100644
--- 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>

@@ -48,16 +49,24 @@ 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;
+
+ 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);
+ ret = seq_has_overflowed(m);
+ if (ret)
+ goto out;
+
+ if (file->f_op->show_fdinfo)
+ file->f_op->show_fdinfo(m, file);
+ ret = seq_has_overflowed(m);

+out:
+ fput(file);
return ret;
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b4d71b5..ba0bd2a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1018,6 +1018,9 @@ 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)
@@ -1154,6 +1157,10 @@ 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 */


--
2.1.0


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