Re: [PATCH v4 14/15] livepatch: add /proc/<pid>/patch_state

On Tue, Jan 31, 2017 at 03:31:39PM +0100, Miroslav Benes wrote:

On Thu, 19 Jan 2017, Josh Poimboeuf wrote:

quoted

Expose the per-task patch state value so users can determine which tasks
are holding up completion of a patching operation.

Signed-off-by: Josh Poimboeuf <redacted>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
---
 Documentation/filesystems/proc.txt | 18 ++++++++++++++++++
 fs/proc/base.c                     | 15 +++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 72624a1..85c501b 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt

@@ -44,6 +44,7 @@ Table of Contents
   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
   3.9   /proc/<pid>/map_files - Information about memory mapped files
   3.10  /proc/<pid>/timerslack_ns - Task timerslack value
+  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
 
   4	Configuring procfs
   4.1	Mount options

@@ -1886,6 +1887,23 @@ Valid values are from 0 - ULLONG_MAX
 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
 permissions on the task specified to change its timerslack_ns value.
 
+3.11	/proc/<pid>/patch_state - Livepatch patch operation state
+-----------------------------------------------------------------
+When CONFIG_LIVEPATCH is enabled, this file displays the value of the
+patch state for the task.
+
+A value of '-1' indicates that no patch is in transition.
+
+A value of '0' indicates that a patch is in transition and the task is
+unpatched.  If the patch is being enabled, then the task hasn't been
+patched yet.  If the patch is being disabled, then the task has already
+been unpatched.
+
+A value of '1' indicates that a patch is in transition and the task is
+patched.  If the patch is being enabled, then the task has already been
+patched.  If the patch is being disabled, then the task hasn't been
+unpatched yet.
+

Despite my review I thought about this some more. I think the logic make 
sense internally but when exposed it can be confusing. We do not export 
klp_target_state value, so users have to know if a patch is being enabled 
or disabled. Of course, they should know that, but I guess they'd like to 
use an userspace tool for this. Such tool needs to look at 
/proc/<pid>/patch_state to find out which tasks are blocking the 
completion and that is it. No more information anywhere.

We can either export klp_target_state, or change /proc/<pid>/patch_state 
to show only two states - task is in transition (1), task is patched (0).

What do you think?

Isn't this information already available in
/sys/kernel/livepatch/<patch>/{enabled,transition}?

-- 
Josh