linux-kernel - [PATCH] irqdesc: Use bool return type instead of int

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Message-Id: <1512142179-24616-1-git-send-email-will.deacon@arm.com>
Date:   Fri,  1 Dec 2017 15:29:39 +0000
From:   Will Deacon <will.deacon@....com>
To:     tglx@...utronix.de
Cc:     marc.zyngier@....com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, Will Deacon <will.deacon@....com>
Subject: [PATCH] irqdesc: Use bool return type instead of int

The irq_balancing_disabled and irq_is_percpu{,_devid} functions are
clearly intended to return bool like the functions in
kernel/irq/settings.h, but actually return an int containing a masked
value of desc->status_use_accessors. This can lead to subtle breakage
if, for example, the return value is subsequently truncated when
assigned to a narrower type.

As Linus points out:

| In particular, what can (and _has_ happened) is that people end up
| using these functions that return true or false, and they assign the
| result to something like a bitfield (or a char) or whatever.
|
| And the code looks *obviously* correct, when you have things like
|
|      dev->percpu = irq_is_percpu_devid(dev->irq);
|
| and that "percpu" thing is just one status bit among many. It may even
| *work*, because maybe that "percpu" flag ends up not being all that
| important, or it just happens to never be set on the particular
| hardware that people end up testing.
|
| But while it looks obviously correct, and might even work, it's really
| fundamentally broken. Because that "true or false" function didn't
| actually return 0/1, it returned 0 or 0x20000.
|
| And 0x20000 may not fit in a bitmask or a "char" or whatever.

Fix the problem by consistently using bool as the return type for these
functions.

Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@....com>
---
 include/linux/irqdesc.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index dd418955962b..39fb3700f7a9 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -230,7 +230,7 @@ irq_set_chip_handler_name_locked(struct irq_data *data, struct irq_chip *chip,
 	data->chip = chip;
 }

-static inline int irq_balancing_disabled(unsigned int irq)
+static inline bool irq_balancing_disabled(unsigned int irq)
 {
 	struct irq_desc *desc;

@@ -238,7 +238,7 @@ static inline int irq_balancing_disabled(unsigned int irq)
 	return desc->status_use_accessors & IRQ_NO_BALANCING_MASK;
 }

-static inline int irq_is_percpu(unsigned int irq)
+static inline bool irq_is_percpu(unsigned int irq)
 {
 	struct irq_desc *desc;

@@ -246,7 +246,7 @@ static inline int irq_is_percpu(unsigned int irq)
 	return desc->status_use_accessors & IRQ_PER_CPU;
 }

-static inline int irq_is_percpu_devid(unsigned int irq)
+static inline bool irq_is_percpu_devid(unsigned int irq)
 {
 	struct irq_desc *desc;

-- 
2.1.4