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SubjectRe: [PATCH] docs: kernel-hacking: discourage from calling disable_irq() in atomic
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Hi Alexander,

On 12/12/22 17:37, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
>
> Correct the example in documentation so that disable_irq() is not being
> called in atomic context and remove the comment allowing to do so "with
> care" from the function header itself.
>
> disable_irq() calls sleeping synchronize_irq(), it's not allowed to call
> them in atomic context.
>
> Link: https://lore.kernel.org/lkml/87k02wbs2n.ffs@tglx/
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Reviewed-by: Manfred Spraul <manfred@colorfullife.com>

(but check below, I would prefer if the change to kernel/irq/manage.c is
dropped.

> ---
> Documentation/kernel-hacking/locking.rst | 4 ++--
> Documentation/translations/it_IT/kernel-hacking/locking.rst | 4 ++--
> kernel/irq/manage.c | 2 --
> 3 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
> index 6805ae6e86e65..95fd6e0900d92 100644
> --- a/Documentation/kernel-hacking/locking.rst
> +++ b/Documentation/kernel-hacking/locking.rst
> @@ -1274,11 +1274,11 @@ Manfred Spraul points out that you can still do this, even if the data
> is very occasionally accessed in user context or softirqs/tasklets. The
> irq handler doesn't use a lock, and all other accesses are done as so::
>
> - spin_lock(&lock);
> + mutex_lock(&lock);
> disable_irq(irq);
> ...
> enable_irq(irq);
> - spin_unlock(&lock);
> + mutex_unlock(&lock);
>
> The disable_irq() prevents the irq handler from running
> (and waits for it to finish if it's currently running on other CPUs).
> diff --git a/Documentation/translations/it_IT/kernel-hacking/locking.rst b/Documentation/translations/it_IT/kernel-hacking/locking.rst
> index 51af37f2d6210..bfbada56cf351 100644
> --- a/Documentation/translations/it_IT/kernel-hacking/locking.rst
> +++ b/Documentation/translations/it_IT/kernel-hacking/locking.rst
> @@ -1309,11 +1309,11 @@ se i dati vengono occasionalmente utilizzati da un contesto utente o
> da un'interruzione software. Il gestore d'interruzione non utilizza alcun
> *lock*, e tutti gli altri accessi verranno fatti così::
>
> - spin_lock(&lock);
> + mutex_lock(&lock);
> disable_irq(irq);
> ...
> enable_irq(irq);
> - spin_unlock(&lock);
> + mutex_unlock(&lock);
>
> La funzione disable_irq() impedisce al gestore d'interruzioni
> d'essere eseguito (e aspetta che finisca nel caso fosse in esecuzione su

> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 40fe7806cc8c9..2054de5bf3c53 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -722,8 +722,6 @@ EXPORT_SYMBOL(disable_irq_nosync);
> * This function waits for any pending IRQ handlers for this interrupt
> * to complete before returning. If you use this function while
> * holding a resource the IRQ handler may need you will deadlock.
> - *
> - * This function may be called - with care - from IRQ context.
> */
> void disable_irq(unsigned int irq)
> {

Can you drop this part?

I haven't noticed that you added this change into the patch, and thus I
created a seperate patch.

https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kernel-irq-managec-disable_irq-might-sleep.patch

As core difference: I've added a might_sleep() into disable_irq().


--

    Manfred

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