Linux-rt-users archive on lore.kernel.org
 help / color / Atom feed
From: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
To: Tom Zanussi <zanussi@kernel.org>, Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	John Kacur <jkacur@redhat.com>, Julia Cartwright <julia@ni.com>,
	Daniel Wagner <wagi@monom.org>,
	Julien Grall <julien.grall@arm.com>
Subject: Re: [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base
Date: Tue, 28 Apr 2020 08:51:35 +0200
Message-ID: <48699adb-73f9-225c-c8f4-959f4b3008b3@prevas.dk> (raw)
In-Reply-To: <2535a046bc15f28478c5289742e617a468becbd6.camel@kernel.org>

On 27/04/2020 21.26, Tom Zanussi wrote:
> On Mon, 2020-04-27 at 15:06 -0400, Steven Rostedt wrote:
>> On Mon, 27 Apr 2020 15:10:00 +0200
>> Rasmus Villemoes <rasmus.villemoes@prevas.dk> wrote:
>>
>>> Reverting
>>>
>>> b1a471ec4df1 - hrtimer: Prevent using hrtimer_grab_expiry_lock() on
>>> migration_base
>>> 40aae5708e7a - hrtimer: Add a missing bracket and hide
>>> `migration_base'
>>> on !SMP
>>>
>>> on top of v4.19.94-rt39 makes that problem go away, i.e. the board
>>> reboots as expected.
>>>
>> Thanks Rasmus for looking into this. Tom now maintains 4.19-rt.
>>
>> Tom, care to pull in these patches on top of 4.19-rt?
>>
> 
> Those patches are already in 4.19-rt - he's saying that reverting them
> fixes the problem.
> 
> I'm guessing that the assumption of base or base->cpu_base always being
> non-NULL in those patches might be wrong.  If so, the below patch
> should fix the problem:
> 
> Subject: [PATCH] hrtimer: Add back base and base->cpu_base checks in
>  hrtimer_grab_expiry_lock()
> 
> 4.19 commit b1a471ec4df1 [hrtimer: Prevent using
> hrtimer_grab_expiry_lock() on migration_base] removed the NULL checks
> for timer->base and timer->base->cpu_base on the assumption that
> they're always non-NULL.  That assumption is apparently not to be
> true, so add the checks back.
> 
> Signed-off-by: Tom Zanussi <zanussi@kernel.org>
> ---
>  kernel/time/hrtimer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index e54a95de8b79..6f20cf23008b 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -953,7 +953,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
>  {
>  	struct hrtimer_clock_base *base = READ_ONCE(timer->base);
>  
> -	if (timer->is_soft && is_migration_base(base)) {
> +	if (timer->is_soft && base && base->cpu_base && is_migration_base(base)) {

I'm sorry, but no, I don't think that can be it. For !SMP (my case),
is_migration_base() is always false, so with or without the above, the
whole if() is false. Also, the symptoms do not look like a NULL pointer
deref, but more like a dead (or live) lock - so I'm guessing (and that's
just a wild guess) that the lock/unlock sequence is needed to give some
other thread a priority boost to make the whole machine make forward
progress.

Rasmus

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-23 20:39 [PATCH RT 00/30] Linux 4.19.94-rt39-rc2 Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 01/30] i2c: exynos5: Remove IRQF_ONESHOT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 02/30] i2c: hix5hd2: " Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 03/30] sched/deadline: Ensure inactive_timer runs in hardirq context Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 04/30] thermal/x86_pkg_temp: make pkg_temp_lock a raw spinlock Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 05/30] dma-buf: Use seqlock_t instread disabling preemption Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 06/30] KVM: arm/arm64: Let the timer expire in hardirq context on RT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 07/30] x86: preempt: Check preemption level before looking at lazy-preempt Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 08/30] hrtimer: Use READ_ONCE to access timer->base in hrimer_grab_expiry_lock() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 09/30] hrtimer: Dont grab the expiry lock for non-soft hrtimer Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base Steven Rostedt
2020-04-27 13:10   ` Rasmus Villemoes
2020-04-27 19:06     ` Steven Rostedt
2020-04-27 19:26       ` Tom Zanussi
2020-04-28  6:51         ` Rasmus Villemoes [this message]
2020-04-28  7:03   ` Rasmus Villemoes
2020-04-28 12:59     ` Tom Zanussi
2020-04-28 13:07       ` Rasmus Villemoes
2020-04-28 13:43         ` Tom Zanussi
2020-01-23 20:39 ` [PATCH RT 11/30] hrtimer: Add a missing bracket and hide `migration_base on !SMP Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 12/30] posix-timers: Unlock expiry lock in the early return Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 14/30] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus_ptr Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 15/30] sched: Remove dead __migrate_disabled() check Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 16/30] sched: migrate disable: Protect cpus_ptr with lock Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 17/30] lib/smp_processor_id: Dont use cpumask_equal() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 18/30] futex: Make the futex_hash_bucket spinlock_t again and bring back its old state Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 19/30] locking/rtmutex: Clean ->pi_blocked_on in the error case Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 20/30] lib/ubsan: Dont seralize UBSAN report Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 21/30] kmemleak: Change the lock of kmemleak_object to raw_spinlock_t Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 22/30] sched: migrate_enable: Use select_fallback_rq() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 23/30] sched: Lazy migrate_disable processing Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 24/30] sched: migrate_enable: Use stop_one_cpu_nowait() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 25/30] Revert "ARM: Initialize split page table locks for vector page" Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 26/30] locking: Make spinlock_t and rwlock_t a RCU section on RT Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 27/30] sched/core: migrate_enable() must access takedown_cpu_task on !HOTPLUG_CPU Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 28/30] lib/smp_processor_id: Adjust check_preemption_disabled() Steven Rostedt
2020-01-23 20:39 ` [PATCH RT 29/30] sched: migrate_enable: Busy loop until the migration request is completed Steven Rostedt
2020-01-23 20:40 ` [PATCH RT 30/30] Linux 4.19.94-rt39-rc2 Steven Rostedt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=48699adb-73f9-225c-c8f4-959f4b3008b3@prevas.dk \
    --to=rasmus.villemoes@prevas.dk \
    --cc=C.Emde@osadl.org \
    --cc=bigeasy@linutronix.de \
    --cc=jkacur@redhat.com \
    --cc=julia@ni.com \
    --cc=julien.grall@arm.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    --cc=wagi@monom.org \
    --cc=zanussi@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-rt-users archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rt-users/0 linux-rt-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rt-users linux-rt-users/ https://lore.kernel.org/linux-rt-users \
		linux-rt-users@vger.kernel.org
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rt-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git