Re: [PATCH] proc: show locks in /proc/pid/fdinfo/X

[Jeff Layton <jlayton@poochiereds.net>]

On Fri, 6 Mar 2015 09:41:00 -0500
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> On Thu, Mar 05, 2015 at 06:37:18PM +0300, Andrey Vagin 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
> 
> The major:minor part is redundant as long as you have the mnt_id, right?
> 
> But I think it makes sense to leave it as you have it, with the same
> format as /proc/locks.  We get to share the kernel code, maybe userland
> gets to reuse a little code too.
> 
> And we should really remove that "ifdef WE_CAN_BREAK_LSLK_NOW" from
> fs/locks.c, clearly that's not going to happen.  (And add a comment that
> the better solution may be to get the mntid from fdinfo, if that's
> true?)
> 

Yeah, I don't see a good reason to keep that in place either. It's been
there since the git history started. I'll queue up a patch to remove it
in v4.1.

Thanks!

> Anyway, that's a digression, ACK to the patch.
> 
> --b.
> 
> > 
> > $ 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


-- 
Jeff Layton <jlayton@poochiereds.net>