handle_nested_irq() is supposed to be running inside the parent thread
handler context. It per se has no dedicated kernel thread, thus shouldn't
touch desc->threads_active. The parent kernel thread has already taken
care of this.
Fixes: e2c12739ccf7 ("genirq: Prevent nested thread vs synchronize_hardirq() deadlock")
Cc: [email protected]
Signed-off-by: Peng Liu <[email protected]>
---
Despite of its correctness, I'm afraid the testing on my only PC can't
cover the affected code path. So the patch may be totally -UNTESTED-.
kernel/irq/chip.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index dc94e0bf2c94..85d4f29134e9 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -478,7 +478,6 @@ void handle_nested_irq(unsigned int irq)
}
kstat_incr_irqs_this_cpu(desc);
- atomic_inc(&desc->threads_active);
raw_spin_unlock_irq(&desc->lock);
action_ret = IRQ_NONE;
@@ -487,8 +486,6 @@ void handle_nested_irq(unsigned int irq)
if (!irq_settings_no_debug(desc))
note_interrupt(desc, action_ret);
-
- wake_threads_waitq(desc);
}
EXPORT_SYMBOL_GPL(handle_nested_irq);
--
2.39.2
On Mon, Jun 10 2024 at 02:30, Peng Liu wrote:
> handle_nested_irq() is supposed to be running inside the parent thread
> handler context. It per se has no dedicated kernel thread, thus shouldn't
> touch desc->threads_active. The parent kernel thread has already taken
> care of this.
No it has not. The parent thread has marked itself in the parent threads
interrupt descriptor.
How does that help synchronizing the nested interrupt, which has a
separate interrupt descriptor?
> Fixes: e2c12739ccf7 ("genirq: Prevent nested thread vs synchronize_hardirq() deadlock")
> Cc: [email protected]
There is nothing to fix.
> Signed-off-by: Peng Liu <[email protected]>
> ---
>
> Despite of its correctness, I'm afraid the testing on my only PC can't
> cover the affected code path. So the patch may be totally -UNTESTED-.
Which correctness?
The change log of the commit you want to "fix" says:
Remove the incorrect usage in the nested threaded interrupt case and
instead re-use the threads_active / wait_for_threads mechanism to
wait for nested threaded interrupts to complete.
It's very clearly spelled out, no?
Thanks,
tglx
On Mon, Jun 10, 2024 at 08:23:09PM +0200, Thomas Gleixner wrote:
> On Mon, Jun 10 2024 at 02:30, Peng Liu wrote:
> > handle_nested_irq() is supposed to be running inside the parent thread
> > handler context. It per se has no dedicated kernel thread, thus shouldn't
> > touch desc->threads_active. The parent kernel thread has already taken
> > care of this.
>
> No it has not. The parent thread has marked itself in the parent threads
> interrupt descriptor.
>
> How does that help synchronizing the nested interrupt, which has a
> separate interrupt descriptor?
Right, I never thought there would be more than one interrupt
descriptors involved which is quite common.
>
> > Fixes: e2c12739ccf7 ("genirq: Prevent nested thread vs synchronize_hardirq() deadlock")
> > Cc: [email protected]
>
> There is nothing to fix.
>
> > Signed-off-by: Peng Liu <[email protected]>
> > ---
> >
> > Despite of its correctness, I'm afraid the testing on my only PC can't
> > cover the affected code path. So the patch may be totally -UNTESTED-.
>
> Which correctness?
>
> The change log of the commit you want to "fix" says:
>
> Remove the incorrect usage in the nested threaded interrupt case and
> instead re-use the threads_active / wait_for_threads mechanism to
> wait for nested threaded interrupts to complete.
>
> It's very clearly spelled out, no?
Indeed, due to my ignorance, I never thought there might be more
descriptors involved. Now think about it, I never really understood
the meaning of the above change log.
Thanks for your time and concise explanation.
Peng
>
> Thanks,
>
> tglx