linux-kernel - [PATCH] docs: kernel-hacking: discourage from calling disable

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Date:   Mon, 12 Dec 2022 17:37:15 +0100
From:   "A. Sverdlin" <alexander.sverdlin@...mens.com>
To:     linux-doc@...r.kernel.org
Cc:     Alexander Sverdlin <alexander.sverdlin@...mens.com>,
        Jonathan Corbet <corbet@....net>,
        Federico Vaga <federico.vaga@...a.pv.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Manfred Spraul <manfred@...orfullife.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] docs: kernel-hacking: discourage from calling disable_irq() in atomic

From: Alexander Sverdlin <alexander.sverdlin@...mens.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@...mens.com>
---
 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)
 {
-- 
2.34.1