On Tue, 2017-06-06 at 13:19 -0400, Benjamin Coddington wrote:
> Since commit c69899a17ca4 "NFSv4: Update of VFS byte range lock must be
> atomic with the stateid update", NFSv4 has been inserting locks in rpciod
> worker context. The result is that the file_lock's fl_nspid is the
> kworker's pid instead of the original userspace pid.
>
> The fl_nspid is only used to represent the namespaced virtual pid number
> when displaying locks or returning from F_GETLK. There's no reason to set
> it for every inserted lock, since we can usually just look it up from
> fl_pid. So, instead of looking up and holding struct pid for every lock,
> let's just look up the virtual pid number from fl_pid when it is needed.
> That means we can remove fl_nspid entirely.
>
With this set, I think we ought to codify that the stored pid must be
relative
> Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> ---
> fs/locks.c | 58 ++++++++++++++++++++++++++++++++----------------------
> include/linux/fs.h | 1 -
> 2 files changed, 35 insertions(+), 24 deletions(-)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index d7daa6c8932f..104398ccc9b9 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -733,7 +733,6 @@ static void locks_wake_up_blocks(struct file_lock *blocker)
> static void
> locks_insert_lock_ctx(struct file_lock *fl, struct list_head *before)
> {
> - fl->fl_nspid = get_pid(task_tgid(current));
> list_add_tail(&fl->fl_list, before);
> locks_insert_global_locks(fl);
> }
> @@ -743,10 +742,6 @@ locks_unlink_lock_ctx(struct file_lock *fl)
> {
> locks_delete_global_locks(fl);
> list_del_init(&fl->fl_list);
> - if (fl->fl_nspid) {
> - put_pid(fl->fl_nspid);
> - fl->fl_nspid = NULL;
> - }
> locks_wake_up_blocks(fl);
> }
>
> @@ -823,8 +818,6 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
> list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
> if (posix_locks_conflict(fl, cfl)) {
> locks_copy_conflock(fl, cfl);
> - if (cfl->fl_nspid)
> - fl->fl_pid = pid_vnr(cfl->fl_nspid);
> goto out;
> }
> }
> @@ -2048,6 +2041,31 @@ int vfs_test_lock(struct file *filp, struct file_lock *fl)
> }
> EXPORT_SYMBOL_GPL(vfs_test_lock);
>
> +/**
> + * locks_translate_pid - translate a pid number into a namespace
> + * @nr: The pid number in the init_pid_ns
> + * @ns: The namespace into which the pid should be translated
> + *
> + * Used to tranlate a fl_pid into a namespace virtual pid number
> + */
> +static pid_t locks_translate_pid(int init_nr, struct pid_namespace *ns)
> +{
> + pid_t vnr = 0;
> + struct task_struct *task;
> +
> + rcu_read_lock();
> + task = find_task_by_pid_ns(init_nr, &init_pid_ns);
> + if (task)
> + get_task_struct(task);
> + rcu_read_unlock();
Is that safe? What prevents get_task_struct from doing a 0->1 transition
there after the task usage count has already gone 1->0 and is on its way
to being freed?
> + if (!task)
> + goto out;
> + vnr = task_pid_nr_ns(task, ns);
> + put_task_struct(task);
> +out:
> + return vnr;
> +}
> +
> static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
> {
> flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
> @@ -2584,22 +2602,16 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
> {
> struct inode *inode = NULL;
> unsigned int fl_pid;
> + struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
>
> - if (fl->fl_nspid) {
> - struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
> -
> - /* Don't let fl_pid change based on who is reading the file */
> - fl_pid = pid_nr_ns(fl->fl_nspid, proc_pidns);
> -
> - /*
> - * If there isn't a fl_pid don't display who is waiting on
> - * the lock if we are called from locks_show, or if we are
> - * called from __show_fd_info - skip lock entirely
> - */
> - if (fl_pid == 0)
> - return;
> - } else
> - fl_pid = fl->fl_pid;
> + fl_pid = locks_translate_pid(fl->fl_pid, proc_pidns);
> + /*
> + * If there isn't a fl_pid don't display who is waiting on
> + * the lock if we are called from locks_show, or if we are
> + * called from __show_fd_info - skip lock entirely
> + */
> + if (fl_pid == 0)
> + return;
>
> if (fl->fl_file != NULL)
> inode = locks_inode(fl->fl_file);
> @@ -2674,7 +2686,7 @@ static int locks_show(struct seq_file *f, void *v)
>
> fl = hlist_entry(v, struct file_lock, fl_link);
>
> - if (fl->fl_nspid && !pid_nr_ns(fl->fl_nspid, proc_pidns))
> + if (locks_translate_pid(fl->fl_pid, proc_pidns) == 0)
> return 0;
>
> lock_get_status(f, fl, iter->li_pos, "");
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index aa4affb38c39..b013fac515f7 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -984,7 +984,6 @@ struct file_lock {
> unsigned char fl_type;
> unsigned int fl_pid;
> int fl_link_cpu; /* what cpu's list is this on? */
> - struct pid *fl_nspid;
> wait_queue_head_t fl_wait;
> struct file *fl_file;
> loff_t fl_start;
--
Jeff Layton <jlayton@xxxxxxxxxx>
