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Message-ID: <20150306144100.GA24137@fieldses.org>
Date: Fri, 6 Mar 2015 09:41:00 -0500
From: "J. Bruce Fields" <bfields@...ldses.org>
To: Andrey Vagin <avagin@...nvz.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
Alexander Viro <viro@...iv.linux.org.uk>,
Jeff Layton <jlayton@...chiereds.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] proc: show locks in /proc/pid/fdinfo/X
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?)
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@....net>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Jeff Layton <jlayton@...chiereds.net>
> Cc: "J. Bruce Fields" <bfields@...ldses.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Signed-off-by: Andrey Vagin <avagin@...nvz.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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