On Wed, Mar 11, 2015 at 03:08:53PM -0700, Andrew Morton wrote:
> On Thu, 5 Mar 2015 18:37:18 +0300 Andrey Vagin <avagin@xxxxxxxxxx> wrote:
>
> > 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.
> >
> > ...
> >
> > --- 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;
>
> seq_has_overflowed() returns a boolean, but fs/seq_file.c:traverse() is
> looking for a -ve errno from ->show().
>
> Documentation/filesystems/seq_file.txt says
>
> If all is well, the show() function should return zero. A negative error
> code in the usual manner indicates that something went wrong; it will be
> passed back to user space. This function can also return SEQ_SKIP, which
> causes the current item to be skipped; if the show() function has already
> generated output before returning SEQ_SKIP, that output will be dropped.
You are right. The updated version of this patch is attached. Thank you
for the review.
>
>
> > + if (file->f_op->show_fdinfo)
> > + file->f_op->show_fdinfo(m, file);
> > + ret = seq_has_overflowed(m);
> >
> > +out:
> > + fput(file);
> > return ret;
> > }
>
>From 29fcabc8a9d9c8bea4a7ec6202a7c0f6e98a518e Mon Sep 17 00:00:00 2001
From: Andrey Vagin <avagin@xxxxxxxxxx>
Date: Thu, 26 Feb 2015 15:46:02 +0300
Subject: [PATCH] proc: show locks in /proc/pid/fdinfo/X (v2)
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.
v1:
Acked-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Acked-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Acked-by: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
v2: use seq_has_overflowed() properly
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
---
Documentation/filesystems/proc.txt | 4 ++++
fs/locks.c | 38 ++++++++++++++++++++++++++++++++++++++
fs/proc/fd.c | 27 +++++++++++++++++----------
include/linux/fs.h | 7 +++++++
4 files changed, 66 insertions(+), 10 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 f1bad68..89a0540 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2593,6 +2593,44 @@ 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
--- 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 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
