The patch titled
Subject: include/linux/percpu_counter.h: race in uniprocessor percpu_counter_add()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
include-linux-percpu_counterh-race-in-uniprocessor-percpu_counter_add.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/include-linux-percpu_counterh-race-in-uniprocessor-percpu_counter_add.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Subject: include/linux/percpu_counter.h: race in uniprocessor percpu_counter_add()
Date: Fri, 16 Dec 2022 16:04:40 +0100
The percpu interface is supposed to be preempt and irq safe.
But:
The uniprocessor implementation of percpu_counter_add() is not irq safe:
if an interrupt happens during the +=, then the result is undefined.
Therefore: switch from preempt_disable() to local_irq_save().
This prevents interrupts from interrupting the +=, and as a side effect
prevents preemption.
Link: https://lkml.kernel.org/r/20221216150441.200533-2-manfred@xxxxxxxxxxxxxxxx
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: "Sun, Jiebin" <jiebin.sun@xxxxxxxxx>
Cc: <1vier1@xxxxxx>
Cc: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/percpu_counter.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/include/linux/percpu_counter.h~include-linux-percpu_counterh-race-in-uniprocessor-percpu_counter_add
+++ a/include/linux/percpu_counter.h
@@ -152,9 +152,11 @@ __percpu_counter_compare(struct percpu_c
static inline void
percpu_counter_add(struct percpu_counter *fbc, s64 amount)
{
- preempt_disable();
+ unsigned long flags;
+
+ local_irq_save(flags);
fbc->count += amount;
- preempt_enable();
+ local_irq_restore(flags);
}
/* non-SMP percpu_counter_add_local is the same with percpu_counter_add */
_
Patches currently in -mm which might be from manfred@xxxxxxxxxxxxxxxx are
lib-percpu_counter-percpu_counter_add_batch-overflow-underflow.patch
include-linux-percpu_counterh-race-in-uniprocessor-percpu_counter_add.patch
kernel-irq-managec-disable_irq-might-sleep.patch
