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[PATCH 0/3 v3] Fixups for l_pid

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  [PATCH 0/3 v3] Fixups for l_pid Benjamin Coddington <bcodding@redhat.com> - 2017-06-06 19:30 +0200
    [PATCH 3/3] fs/locks: Use fs-specific l_pid for remote locks Benjamin Coddington <bcodding@redhat.com> - 2017-06-06 19:30 +0200
    [PATCH 2/3] fs/locks: Remove fl_nspid Benjamin Coddington <bcodding@redhat.com> - 2017-06-06 19:30 +0200
      Re: [PATCH 2/3] fs/locks: Remove fl_nspid Jeff Layton <jlayton@redhat.com> - 2017-06-06 20:10 +0200
        Re: [PATCH 2/3] fs/locks: Remove fl_nspid Jeff Layton <jlayton@redhat.com> - 2017-06-06 20:30 +0200
          Re: [PATCH 2/3] fs/locks: Remove fl_nspid "Benjamin Coddington" <bcodding@redhat.com> - 2017-06-06 21:00 +0200
            Re: [PATCH 2/3] fs/locks: Remove fl_nspid "Benjamin Coddington" <bcodding@redhat.com> - 2017-06-06 22:50 +0200
            Re: [PATCH 2/3] fs/locks: Remove fl_nspid Jeff Layton <jlayton@redhat.com> - 2017-06-07 01:10 +0200

#1658965 — [PATCH 0/3 v3] Fixups for l_pid

LTP fcntl tests (fcntl11 fcntl14 fcntl17 fcntl19 fcntl20 fcntl21) have been
failing for NFSv4 mounts due to an unexpected l_pid.  What follows are some
fixups:

v2: - Rebase onto linux-next
    - Revert back to using the stack in locks_mandatory_area(), and fixup
	patch description for 1/3

v3: - The lkp-robot found some serious per_thread_ops performance
	regressions for v1 and v2, so this version changes things around to not
	acquire a reference to struct pid in fl_nspid for every lock.  Instead,
	it drops fl_nspid altogether, and defers the lookup of the
	namespace-translated pid until it actually needed.

Benjamin Coddington (3):
  fs/locks: Use allocation rather than the stack in fcntl_getlk()
  fs/locks: Remove fl_nspid
  fs/locks: Use fs-specific l_pid for remote locks

 fs/locks.c         | 122 +++++++++++++++++++++++++++++++++--------------------
 include/linux/fs.h |   2 +-
 2 files changed, 78 insertions(+), 46 deletions(-)

-- 
2.9.3

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#1658967 — [PATCH 3/3] fs/locks: Use fs-specific l_pid for remote locks

Now that we're translating fl_pid for F_GETLK and /proc/locks, we need to
handle the case where a remote filesystem directly sets fl_pid.  In that
case, the fl_pid should not be translated into a local pid namespace.  If
the filesystem implements the lock operation, set a flag to return the
lock's fl_pid value directly, rather translate it.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
---
 fs/locks.c         | 22 ++++++++++++++++++----
 include/linux/fs.h |  1 +
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 104398ccc9b9..6858ec9802d2 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2034,8 +2034,10 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
  */
 int vfs_test_lock(struct file *filp, struct file_lock *fl)
 {
-	if (filp->f_op->lock && is_remote_lock(filp))
+	if (filp->f_op->lock && is_remote_lock(filp)) {
+		fl->fl_flags |= FL_PID_PRIV;
 		return filp->f_op->lock(filp, F_GETLK, fl);
+	}
 	posix_test_lock(filp, fl);
 	return 0;
 }
@@ -2066,9 +2068,18 @@ static pid_t locks_translate_pid(int init_nr, struct pid_namespace *ns)
 	return vnr;
 }
 
+static pid_t flock_translate_pid(struct file_lock *fl)
+{
+	if (IS_OFDLCK(fl))
+		return -1;
+	if (fl->fl_flags & FL_PID_PRIV)
+		return fl->fl_pid;
+	return locks_translate_pid(fl->fl_pid,  task_active_pid_ns(current));
+}
+
 static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 {
-	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
+	flock->l_pid = flock_translate_pid(fl);
 #if BITS_PER_LONG == 32
 	/*
 	 * Make sure we can represent the posix lock via
@@ -2090,7 +2101,7 @@ static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 #if BITS_PER_LONG == 32
 static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
 {
-	flock->l_pid = IS_OFDLCK(fl) ? -1 : fl->fl_pid;
+	flock->l_pid = flock_translate_pid(fl);
 	flock->l_start = fl->fl_start;
 	flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
 		fl->fl_end - fl->fl_start + 1;
@@ -2604,7 +2615,10 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
 	unsigned int fl_pid;
 	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
 
-	fl_pid = locks_translate_pid(fl->fl_pid, proc_pidns);
+	if (fl->fl_flags & FL_PID_PRIV)
+		fl_pid = fl->fl_pid;
+	else
+		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
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b013fac515f7..179496a9719d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -908,6 +908,7 @@ static inline struct file *get_file(struct file *f)
 #define FL_UNLOCK_PENDING	512 /* Lease is being broken */
 #define FL_OFDLCK	1024	/* lock is "owned" by struct file */
 #define FL_LAYOUT	2048	/* outstanding pNFS layout */
+#define FL_PID_PRIV	4096	/* F_GETLK should report fl_pid */
 
 #define FL_CLOSE_POSIX (FL_POSIX | FL_CLOSE)
 
-- 
2.9.3

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#1658971 — [PATCH 2/3] fs/locks: Remove fl_nspid

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.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
---
 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();
+	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;
-- 
2.9.3

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#1659020 — Re: [PATCH 2/3] fs/locks: Remove fl_nspid

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@redhat.com>
> ---
>  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@redhat.com>

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#1659035 — Re: [PATCH 2/3] fs/locks: Remove fl_nspid

On Tue, 2017-06-06 at 14:00 -0400, Jeff Layton wrote:
> 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 

...to the init_pid_ns. Let's make that clear in the comments for
filesystem authors.

> 
> 
> > Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> > ---
> >  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;
> > +}


Now that I look, I think it might be best to just do all of that under
the rcu_read_lock and don't muck with the refcount at all. So something
like:

+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)
+               vnr = task_pid_nr_ns(task, ns);
+       rcu_read_unlock();
+       return vnr;
+}

That should be fine since task_pid_nr_ns pretty much does all of its
work under the rcu_read_lock anyway.


> >  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@redhat.com>

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#1659061 — Re: [PATCH 2/3] fs/locks: Remove fl_nspid

On 6 Jun 2017, at 14:25, Jeff Layton wrote:

> On Tue, 2017-06-06 at 14:00 -0400, Jeff Layton wrote:
>> 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
>
> ...to the init_pid_ns. Let's make that clear in the comments for
> filesystem authors.

OK, but I think you mean fl_pid should always be current->tgid or the 
pid as
it is in init_pid_ns.  We translate that pid into the virtual pid of the
process doing F_GETLK or reading /proc/locks.

>>> Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
>>> ---
>>>  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?

Uh, no -- seems not safe.  I copied that directly from fs/proc/base.c, 
and
seems a problem there too.

Changing this to the below avoids the race with the struct task being
released:

rcu_read_lock();
struct pid = find_pid_ns(init_nr, &init_pid_ns)
vnr = pid_vnr(pid);
rcu_read_unlock();

Ben

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#1659189 — Re: [PATCH 2/3] fs/locks: Remove fl_nspid

On 6 Jun 2017, at 14:57, Benjamin Coddington wrote:

> On 6 Jun 2017, at 14:25, Jeff Layton wrote:
>
>> On Tue, 2017-06-06 at 14:00 -0400, Jeff Layton wrote:
>>> 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
>>
>> ...to the init_pid_ns. Let's make that clear in the comments for
>> filesystem authors.
>
> OK, but I think you mean fl_pid should always be current->tgid or the 
> pid as
> it is in init_pid_ns.  We translate that pid into the virtual pid of 
> the
> process doing F_GETLK or reading /proc/locks.

And in that sense, we shouldn't have to add a comment, because the 
expected
behavior is the same as it is today -- namely that fl_pid is 
current->tgid,
or the real pid number, which is the pid number in init_pid_ns.

So, unless you feel strongly that this should be explained in a comment, 
I
think I'll resend this without additional comments after making the 
change
to use find_pid_ns().

Ben

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#1659284 — Re: [PATCH 2/3] fs/locks: Remove fl_nspid

On Tue, 2017-06-06 at 14:57 -0400, Benjamin Coddington wrote:
> On 6 Jun 2017, at 14:25, Jeff Layton wrote:
> 
> > On Tue, 2017-06-06 at 14:00 -0400, Jeff Layton wrote:
> > > 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
> > 
> > ...to the init_pid_ns. Let's make that clear in the comments for
> > filesystem authors.
> 
> OK, but I think you mean fl_pid should always be current->tgid or the 
> pid as
> it is in init_pid_ns.  We translate that pid into the virtual pid of the
> process doing F_GETLK or reading /proc/locks.
> 
> > > > Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> > > > ---
> > > >  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?
> 
> Uh, no -- seems not safe.  I copied that directly from fs/proc/base.c, 
> and
> seems a problem there too.
> 
> Changing this to the below avoids the race with the struct task being
> released:
> 
> rcu_read_lock();
> struct pid = find_pid_ns(init_nr, &init_pid_ns)
> vnr = pid_vnr(pid);
> rcu_read_unlock();
> 

Actually now that I've looked a little more closely, I think it may be
ok. call_rcu callback is what ends up putting the last reference when
the task is released, so if you can find the thing via
find_task_by_pid_ns, then you know that the refcount is at least 1 until
the rcu_read_lock is dropped.

Still, I think doing the pid assignment under rcu_read_lock and not
bothering with the refcount is better in this case...

Thanks,
-- 
Jeff Layton <jlayton@redhat.com>

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