* [PATCH] printk: defer_console_output: do not assume interrupts disabled
@ 2022-02-03 11:29 John Ogness
2022-02-03 11:33 ` Sebastian Andrzej Siewior
2022-02-04 7:04 ` Sergey Senozhatsky
0 siblings, 2 replies; 11+ messages in thread
From: John Ogness @ 2022-02-03 11:29 UTC (permalink / raw)
To: Petr Mladek
Cc: Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
With commit 458df9fd4815 ("printk: remove separate printk_sched
buffers and use printk buf instead") defer_console_output() was
changed to no longer disable interrupts. However, it used the
function __this_cpu_or(), which assumes interrupts disabled. That
also should have been changed to this_cpu_or().
Although defer_console_output() is mostly used when interrupts are
disabled, this is not always the case. One example is
get_random_bytes(), which is often called with interrupts enabled.
get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf3c2aa..164ccdb9423e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3262,7 +3262,7 @@ void defer_console_output(void)
return;
preempt_disable();
- __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+ this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}
base-commit: 88808fbbead481aedb46640a5ace69c58287f56a
--
2.30.2
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH] printk: defer_console_output: do not assume interrupts disabled
2022-02-03 11:29 [PATCH] printk: defer_console_output: do not assume interrupts disabled John Ogness
@ 2022-02-03 11:33 ` Sebastian Andrzej Siewior
2022-02-04 7:04 ` Sergey Senozhatsky
1 sibling, 0 replies; 11+ messages in thread
From: Sebastian Andrzej Siewior @ 2022-02-03 11:33 UTC (permalink / raw)
To: John Ogness; +Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, linux-kernel
On 2022-02-03 12:35:15 [+0106], John Ogness wrote:
> With commit 458df9fd4815 ("printk: remove separate printk_sched
> buffers and use printk buf instead") defer_console_output() was
> changed to no longer disable interrupts. However, it used the
> function __this_cpu_or(), which assumes interrupts disabled. That
> also should have been changed to this_cpu_or().
>
> Although defer_console_output() is mostly used when interrupts are
> disabled, this is not always the case. One example is
> get_random_bytes(), which is often called with interrupts enabled.
It is okay for __this_cpu_or() to be invoked with disabled preemption if
that is true for all callers. Disabled interrupts or not is not
important as long as there are no callers in_irq(). I believe that there
are callers in_irq() and therefore this_cpu_or() is correct.
> get_random_bytes()
> warn_unseeded_randomness()
> printk_deferred()
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Sebastian
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] printk: defer_console_output: do not assume interrupts disabled
2022-02-03 11:29 [PATCH] printk: defer_console_output: do not assume interrupts disabled John Ogness
2022-02-03 11:33 ` Sebastian Andrzej Siewior
@ 2022-02-04 7:04 ` Sergey Senozhatsky
2022-02-07 9:46 ` [PATCH v2] printk: defer_console_output: use atomic update John Ogness
1 sibling, 1 reply; 11+ messages in thread
From: Sergey Senozhatsky @ 2022-02-04 7:04 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
On (22/02/03 12:35), John Ogness wrote:
> With commit 458df9fd4815 ("printk: remove separate printk_sched
> buffers and use printk buf instead") defer_console_output() was
> changed to no longer disable interrupts. However, it used the
> function __this_cpu_or(), which assumes interrupts disabled. That
> also should have been changed to this_cpu_or().
>
> Although defer_console_output() is mostly used when interrupts are
> disabled, this is not always the case. One example is
> get_random_bytes(), which is often called with interrupts enabled.
>
> get_random_bytes()
> warn_unseeded_randomness()
> printk_deferred()
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2] printk: defer_console_output: use atomic update
2022-02-04 7:04 ` Sergey Senozhatsky
@ 2022-02-07 9:46 ` John Ogness
2022-02-10 15:47 ` Petr Mladek
0 siblings, 1 reply; 11+ messages in thread
From: John Ogness @ 2022-02-07 9:46 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:
get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
defer_console_output()
and can be updated from interrupt contexts, such as:
handle_irq_event_percpu()
__irq_wake_thread()
wake_up_process()
try_to_wake_up()
select_task_rq()
select_fallback_rq()
printk_deferred()
defer_console_output()
and can be updated from NMI contexts, such as:
vprintk()
if (in_nmi()) defer_console_output()
Therefore this_cpu_or(), the atomic variant of __this_cpu_or(),
should be used to update the variable.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
Change from v1:
Sebastian comments made it clear that the v1 title and message were not
correctly specifying the problem or the reason for the fix. I hope this
text is clearer.
kernel/printk/printk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf3c2aa..164ccdb9423e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3262,7 +3262,7 @@ void defer_console_output(void)
return;
preempt_disable();
- __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+ this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}
base-commit: dfd42facf1e4ada021b939b4e19c935dcdd55566
--
2.30.2
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2] printk: defer_console_output: use atomic update
2022-02-07 9:46 ` [PATCH v2] printk: defer_console_output: use atomic update John Ogness
@ 2022-02-10 15:47 ` Petr Mladek
2022-02-11 11:22 ` John Ogness
0 siblings, 1 reply; 11+ messages in thread
From: Petr Mladek @ 2022-02-10 15:47 UTC (permalink / raw)
To: John Ogness
Cc: Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
On Mon 2022-02-07 10:52:20, John Ogness wrote:
> The per-cpu @printk_pending variable can be updated from
> sleepable contexts, such as:
>
> get_random_bytes()
> warn_unseeded_randomness()
> printk_deferred()
> defer_console_output()
>
> and can be updated from interrupt contexts, such as:
>
> handle_irq_event_percpu()
> __irq_wake_thread()
> wake_up_process()
> try_to_wake_up()
> select_task_rq()
> select_fallback_rq()
> printk_deferred()
> defer_console_output()
>
> and can be updated from NMI contexts, such as:
>
> vprintk()
> if (in_nmi()) defer_console_output()
>
> Therefore this_cpu_or(), the atomic variant of __this_cpu_or(),
> should be used to update the variable.
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Makes sense.
The patch has been committed into printk/linux.git, branch for-5.18.
Best Regards,
Petr
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v2] printk: defer_console_output: use atomic update
2022-02-10 15:47 ` Petr Mladek
@ 2022-02-11 11:22 ` John Ogness
2022-02-11 11:23 ` [PATCH v3] printk: use atomic updates for klogd work John Ogness
2022-02-14 5:32 ` [PATCH v2] printk: defer_console_output: use atomic update Sergey Senozhatsky
0 siblings, 2 replies; 11+ messages in thread
From: John Ogness @ 2022-02-11 11:22 UTC (permalink / raw)
To: Petr Mladek
Cc: Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
Hi Petr,
On 2022-02-10, Petr Mladek <pmladek@suse.com> wrote:
> The patch has been committed into printk/linux.git, branch for-5.18.
Sebastian also pointed out that the use of __this_cpu_xchg() is the same
problem with the same variable for the same reason. We should fold that
change into the patch as well. The patch will followup this message.
@Sergey: I dropped your Reviewed-by since the code changed.
John
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v3] printk: use atomic updates for klogd work
2022-02-11 11:22 ` John Ogness
@ 2022-02-11 11:23 ` John Ogness
2022-02-14 5:35 ` Sergey Senozhatsky
2022-02-15 15:26 ` Petr Mladek
2022-02-14 5:32 ` [PATCH v2] printk: defer_console_output: use atomic update Sergey Senozhatsky
1 sibling, 2 replies; 11+ messages in thread
From: John Ogness @ 2022-02-11 11:23 UTC (permalink / raw)
To: Petr Mladek
Cc: Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:
get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
defer_console_output()
and can be updated from interrupt contexts, such as:
handle_irq_event_percpu()
__irq_wake_thread()
wake_up_process()
try_to_wake_up()
select_task_rq()
select_fallback_rq()
printk_deferred()
defer_console_output()
and can be updated from NMI contexts, such as:
vprintk()
if (in_nmi()) defer_console_output()
Therefore the atomic variant of the updating functions must be used.
Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
Changes:
v3: also fix __this_cpu_xchg() usage
v2: fix commit message
kernel/printk/printk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf3c2aa..c7280b40de6c 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3228,7 +3228,7 @@ static DEFINE_PER_CPU(int, printk_pending);
static void wake_up_klogd_work_func(struct irq_work *irq_work)
{
- int pending = __this_cpu_xchg(printk_pending, 0);
+ int pending = this_cpu_xchg(printk_pending, 0);
if (pending & PRINTK_PENDING_OUTPUT) {
/* If trylock fails, someone else is doing the printing */
@@ -3262,7 +3262,7 @@ void defer_console_output(void)
return;
preempt_disable();
- __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+ this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
}
--
2.30.2
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2] printk: defer_console_output: use atomic update
2022-02-11 11:22 ` John Ogness
2022-02-11 11:23 ` [PATCH v3] printk: use atomic updates for klogd work John Ogness
@ 2022-02-14 5:32 ` Sergey Senozhatsky
2022-02-14 5:35 ` Sergey Senozhatsky
1 sibling, 1 reply; 11+ messages in thread
From: Sergey Senozhatsky @ 2022-02-14 5:32 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
On (22/02/11 12:28), John Ogness wrote:
> Hi Petr,
>
> On 2022-02-10, Petr Mladek <pmladek@suse.com> wrote:
> > The patch has been committed into printk/linux.git, branch for-5.18.
>
> Sebastian also pointed out that the use of __this_cpu_xchg() is the same
> problem with the same variable for the same reason. We should fold that
> change into the patch as well. The patch will followup this message.
But that __this_cpu_xchg() (that this lol) can only be performed form the
IRQ context. Can you please elaborate what is the problem with it?
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v2] printk: defer_console_output: use atomic update
2022-02-14 5:32 ` [PATCH v2] printk: defer_console_output: use atomic update Sergey Senozhatsky
@ 2022-02-14 5:35 ` Sergey Senozhatsky
0 siblings, 0 replies; 11+ messages in thread
From: Sergey Senozhatsky @ 2022-02-14 5:35 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior, Sergey Senozhatsky
On (22/02/14 14:32), Sergey Senozhatsky wrote:
> On (22/02/11 12:28), John Ogness wrote:
> > Hi Petr,
> >
> > On 2022-02-10, Petr Mladek <pmladek@suse.com> wrote:
> > > The patch has been committed into printk/linux.git, branch for-5.18.
> >
> > Sebastian also pointed out that the use of __this_cpu_xchg() is the same
> > problem with the same variable for the same reason. We should fold that
> > change into the patch as well. The patch will followup this message.
>
> But that __this_cpu_xchg() (that this lol) can only be performed form the
> IRQ context. Can you please elaborate what is the problem with it?
Oh, it can race with NMI, yeah.
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v3] printk: use atomic updates for klogd work
2022-02-11 11:23 ` [PATCH v3] printk: use atomic updates for klogd work John Ogness
@ 2022-02-14 5:35 ` Sergey Senozhatsky
2022-02-15 15:26 ` Petr Mladek
1 sibling, 0 replies; 11+ messages in thread
From: Sergey Senozhatsky @ 2022-02-14 5:35 UTC (permalink / raw)
To: John Ogness
Cc: Petr Mladek, Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
On (22/02/11 12:29), John Ogness wrote:
> The per-cpu @printk_pending variable can be updated from
> sleepable contexts, such as:
>
> get_random_bytes()
> warn_unseeded_randomness()
> printk_deferred()
> defer_console_output()
>
> and can be updated from interrupt contexts, such as:
>
> handle_irq_event_percpu()
> __irq_wake_thread()
> wake_up_process()
> try_to_wake_up()
> select_task_rq()
> select_fallback_rq()
> printk_deferred()
> defer_console_output()
>
> and can be updated from NMI contexts, such as:
>
> vprintk()
> if (in_nmi()) defer_console_output()
>
> Therefore the atomic variant of the updating functions must be used.
>
> Replace __this_cpu_xchg() with this_cpu_xchg().
> Replace __this_cpu_or() with this_cpu_or().
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
FWIW
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v3] printk: use atomic updates for klogd work
2022-02-11 11:23 ` [PATCH v3] printk: use atomic updates for klogd work John Ogness
2022-02-14 5:35 ` Sergey Senozhatsky
@ 2022-02-15 15:26 ` Petr Mladek
1 sibling, 0 replies; 11+ messages in thread
From: Petr Mladek @ 2022-02-15 15:26 UTC (permalink / raw)
To: John Ogness
Cc: Sergey Senozhatsky, Steven Rostedt, linux-kernel,
Sebastian Andrzej Siewior
On Fri 2022-02-11 12:29:37, John Ogness wrote:
> The per-cpu @printk_pending variable can be updated from
> sleepable contexts, such as:
>
> get_random_bytes()
> warn_unseeded_randomness()
> printk_deferred()
> defer_console_output()
>
> and can be updated from interrupt contexts, such as:
>
> handle_irq_event_percpu()
> __irq_wake_thread()
> wake_up_process()
> try_to_wake_up()
> select_task_rq()
> select_fallback_rq()
> printk_deferred()
> defer_console_output()
>
> and can be updated from NMI contexts, such as:
>
> vprintk()
> if (in_nmi()) defer_console_output()
>
> Therefore the atomic variant of the updating functions must be used.
>
> Replace __this_cpu_xchg() with this_cpu_xchg().
> Replace __this_cpu_or() with this_cpu_or().
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
The v3 patch is comitted in printk/linux.git, branch for.5.18.
I have replaced v2 version with it.
Best Regards,
Petr
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2022-02-15 15:27 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-02-03 11:29 [PATCH] printk: defer_console_output: do not assume interrupts disabled John Ogness
2022-02-03 11:33 ` Sebastian Andrzej Siewior
2022-02-04 7:04 ` Sergey Senozhatsky
2022-02-07 9:46 ` [PATCH v2] printk: defer_console_output: use atomic update John Ogness
2022-02-10 15:47 ` Petr Mladek
2022-02-11 11:22 ` John Ogness
2022-02-11 11:23 ` [PATCH v3] printk: use atomic updates for klogd work John Ogness
2022-02-14 5:35 ` Sergey Senozhatsky
2022-02-15 15:26 ` Petr Mladek
2022-02-14 5:32 ` [PATCH v2] printk: defer_console_output: use atomic update Sergey Senozhatsky
2022-02-14 5:35 ` Sergey Senozhatsky
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