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

From: Jeff Layton
Date: Sat Mar 07 2015 - 08:00:50 EST

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On Fri, 6 Mar 2015 09:41:00 -0500
"J. Bruce Fields" <bfields@xxxxxxxxxxxx> 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@xxxxxxx>
> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> > Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> > 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, 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@xxxxxxxxxxxxxxx>
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Next message: Sudip Mukherjee: "Re: [PATCH] staging/lustre: Make lstcon_console_{init,fini} static"
Previous message: Peter Hurley: "Re: [PATCH v2 -next 03/13] console: Add extensible console matching"
In reply to: J. Bruce Fields: "Re: [PATCH] proc: show locks in /proc/pid/fdinfo/X"
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