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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Jessica Yu <jeyu@redhat.com>, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
	linux-s390@vger.kernel.org, Vojtech Pavlik <vojtech@suse.com>,
	Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	live-patching@vger.kernel.org, Jiri Slaby <jslaby@suse.cz>,
	linuxppc-dev@lists.ozlabs.org, Ingo Molnar <mingo@kernel.org>,
	Chris J Arges <chris.j.arges@canonical.com>
Subject: Re: [PATCH v3 00/15] livepatch: hybrid consistency model
Date: Sat, 10 Dec 2016 11:17:07 -0600	[thread overview]
Message-ID: <20161210171707.cpupmxyuhob4tc3i@treble> (raw)
In-Reply-To: <1481348777.28041.1.camel@gmail.com>

On Sat, Dec 10, 2016 at 04:46:17PM +1100, Balbir Singh wrote:
> On Thu, 2016-12-08 at 12:08 -0600, Josh Poimboeuf wrote:
> > Dusting the cobwebs off the consistency model again.  This is based on
> > linux-next/master.
> > 
> > v1 was posted on 2015-02-09:
> > 
> >   https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@redhat.com
> > 
> > v2 was posted on 2016-04-28:
> > 
> >   https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@redhat.com
> > 
> > The biggest issue from v2 was finding a decent way to detect preemption
> > and page faults on the stack of a sleeping task.  
> 
> Could you please elaborate on this? Preemption of a sleeping task and
> faults as in the future (time) preemption and faults?

The normal way for a task to go to sleep is to call schedule().  objtool
ensures the stack trace is reliable in that case, by making sure that
all functions save the frame pointer on the stack before calling out to
another function.

But a task can also go to sleep in a few other ways.  One way is by
preemption, where an interrupt handler interrupts the task and calls
preempt_schedule_irq().  Another way is by a page fault exception.  In
both cases, there's no guarantee that the interrupted function saved the
frame pointer on the stack beforehand.  So the stack trace might be
unreliable.  Fortunately, interrupts and exceptions leave evidence
behind on the stack.  So when walking the stack of a sleeping task, we
can detect when an IRQ or exception occurred, and consider such a stack
unreliable.

-- 
Josh

  reply	other threads:[~2016-12-10 17:17 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-08 18:08 [PATCH v3 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces Josh Poimboeuf
2016-12-16 13:07   ` Petr Mladek
2016-12-16 22:09     ` Josh Poimboeuf
2016-12-19 16:25   ` Miroslav Benes
2016-12-19 17:25     ` Josh Poimboeuf
2016-12-19 18:23       ` Miroslav Benes
2016-12-20  9:39       ` Petr Mladek
2016-12-20 21:21         ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 02/15] x86/entry: define _TIF_ALLWORK_MASK flags explicitly Josh Poimboeuf
2016-12-16 14:17   ` Petr Mladek
2016-12-16 22:13     ` Josh Poimboeuf
2016-12-19 16:39   ` Miroslav Benes
2017-01-10  8:49   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 03/15] livepatch: temporary stubs for klp_patch_pending() and klp_update_patch_state() Josh Poimboeuf
2016-12-16 14:41   ` Petr Mladek
2016-12-16 22:15     ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 04/15] livepatch/x86: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2016-12-08 18:27   ` Andy Lutomirski
2016-12-16 15:39   ` Petr Mladek
2016-12-21 13:54   ` Miroslav Benes
2017-01-11  7:06   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 05/15] livepatch/powerpc: " Josh Poimboeuf
2016-12-16 16:00   ` Petr Mladek
2016-12-21 14:30   ` Miroslav Benes
2017-01-10  8:29   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 06/15] livepatch/s390: reorganize TIF thread flag bits Josh Poimboeuf
2016-12-21 15:29   ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 08/15] livepatch: separate enabled and patched states Josh Poimboeuf
2016-12-16 16:21   ` Petr Mladek
2016-12-23 12:54   ` Miroslav Benes
2017-01-10  9:10   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 09/15] livepatch: remove unnecessary object loaded check Josh Poimboeuf
2016-12-16 16:26   ` Petr Mladek
2016-12-23 12:58   ` Miroslav Benes
2017-01-10  9:14   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 10/15] livepatch: move patching functions into patch.c Josh Poimboeuf
2016-12-16 16:49   ` Petr Mladek
2016-12-23 13:06   ` Miroslav Benes
2017-01-10  9:15   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 11/15] livepatch: use kstrtobool() in enabled_store() Josh Poimboeuf
2016-12-16 16:55   ` Petr Mladek
2016-12-16 22:19     ` Josh Poimboeuf
2016-12-23 13:13       ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 12/15] livepatch: store function sizes Josh Poimboeuf
2016-12-19 13:10   ` Petr Mladek
2016-12-23 13:40   ` Miroslav Benes
2017-01-11 10:09   ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 13/15] livepatch: change to a per-task consistency model Josh Poimboeuf
2016-12-20 17:32   ` Petr Mladek
2016-12-21 21:25     ` Josh Poimboeuf
2016-12-22 14:34       ` Petr Mladek
2016-12-22 18:31         ` Josh Poimboeuf
2017-01-10 13:00           ` Petr Mladek
2017-01-10 20:46             ` Josh Poimboeuf
2017-01-11 15:18               ` Petr Mladek
2017-01-11 15:26                 ` Josh Poimboeuf
2016-12-23  9:24       ` Miroslav Benes
2016-12-23 10:18         ` Petr Mladek
2017-01-06 20:07           ` Josh Poimboeuf
2017-01-10 10:40             ` Petr Mladek
2017-01-04 13:44   ` Miroslav Benes
2017-01-06 21:01     ` Josh Poimboeuf
2017-01-10 10:45       ` Miroslav Benes
2017-01-05  9:34   ` Miroslav Benes
2017-01-06 21:04     ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 14/15] livepatch: add /proc/<pid>/patch_state Josh Poimboeuf
2016-12-21 11:20   ` Petr Mladek
2017-01-04 14:50   ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 15/15] livepatch: allow removal of a disabled patch Josh Poimboeuf
2016-12-21 14:44   ` Petr Mladek
2017-01-04 14:57   ` Miroslav Benes
2017-01-06 21:04     ` Josh Poimboeuf
2016-12-10  5:46 ` [PATCH v3 00/15] livepatch: hybrid consistency model Balbir Singh
2016-12-10 17:17   ` Josh Poimboeuf [this message]
2016-12-11  2:08     ` Balbir Singh
2016-12-12 14:04       ` Josh Poimboeuf

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