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Message-ID: <20250803072044.572733-6-ysk@kzalloc.com>
Date: Sun, 3 Aug 2025 07:20:45 +0000
From: Yunseong Kim <ysk@...lloc.com>
To: Dmitry Vyukov <dvyukov@...gle.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Byungchul Park <byungchul@...com>,
max.byungchul.park@...il.com,
Yeoreum Yun <yeoreum.yun@....com>,
ppbuk5246@...il.com,
linux-usb@...r.kernel.org,
linux-rt-devel@...ts.linux.dev,
syzkaller@...glegroups.com,
linux-kernel@...r.kernel.org,
stable@...r.kernel.org,
Yunseong Kim <ysk@...lloc.com>
Subject: [PATCH 2/4] kcov: Replace per-CPU local_lock with local_irq_save/restore
Commit f85d39dd7ed8 ("kcov, usb: disable interrupts in
kcov_remote_start_usb_softirq") introduced a local_irq_save() in the
kcov_remote_start_usb_softirq() wrapper, placing kcov_remote_start() in
atomic context.
The previous patch addressed this by converting the global
kcov_remote_lock to a non-sleeping raw_spinlock_t. However, per-CPU
data in kcov_remote_start() and kcov_remote_stop() remains protected
by kcov_percpu_data.lock, which is a local_lock_t.
On PREEMPT_RT kernels, local_lock_t is implemented as a sleeping lock.
Acquiring it from atomic context triggers warnings or crashes due to
invalid sleeping behavior.
The original use of local_lock_t assumed that kcov_remote_start() would
never be called in atomic context. Now that this assumption no longer
holds, replace it with local_irq_save() and local_irq_restore(), which are
safe in all contexts and compatible with the use of raw_spinlock_t.
With this change, both global and per-CPU synchronization primitives are
guaranteed to be non-sleeping, making kcov_remote_start() safe for
use in atomic contexts.
Signed-off-by: Yunseong Kim <ysk@...lloc.com>
---
kernel/kcov.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)
diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7d9b53385d81..faad3b288ca7 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -90,7 +90,6 @@ static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
struct kcov_percpu_data {
void *irq_area;
- local_lock_t lock;
unsigned int saved_mode;
unsigned int saved_size;
@@ -99,9 +98,7 @@ struct kcov_percpu_data {
int saved_sequence;
};
-static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
- .lock = INIT_LOCAL_LOCK(lock),
-};
+static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data);
/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote *kcov_remote_find(u64 handle)
@@ -862,7 +859,7 @@ void kcov_remote_start(u64 handle)
if (!in_task() && !in_softirq_really())
return;
- local_lock_irqsave(&kcov_percpu_data.lock, flags);
+ local_irq_save(flags);
/*
* Check that kcov_remote_start() is not called twice in background
@@ -870,7 +867,7 @@ void kcov_remote_start(u64 handle)
*/
mode = READ_ONCE(t->kcov_mode);
if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
/*
@@ -879,7 +876,7 @@ void kcov_remote_start(u64 handle)
* happened while collecting coverage from a background thread.
*/
if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
@@ -887,7 +884,7 @@ void kcov_remote_start(u64 handle)
remote = kcov_remote_find(handle);
if (!remote) {
raw_spin_unlock(&kcov_remote_lock);
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
kcov_debug("handle = %llx, context: %s\n", handle,
@@ -912,13 +909,13 @@ void kcov_remote_start(u64 handle)
/* Can only happen when in_task(). */
if (!area) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
area = vmalloc(size * sizeof(unsigned long));
if (!area) {
kcov_put(kcov);
return;
}
- local_lock_irqsave(&kcov_percpu_data.lock, flags);
+ local_irq_save(flags);
}
/* Reset coverage size. */
@@ -930,7 +927,7 @@ void kcov_remote_start(u64 handle)
}
kcov_start(t, kcov, size, area, mode, sequence);
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
}
EXPORT_SYMBOL(kcov_remote_start);
@@ -1004,12 +1001,12 @@ void kcov_remote_stop(void)
if (!in_task() && !in_softirq_really())
return;
- local_lock_irqsave(&kcov_percpu_data.lock, flags);
+ local_irq_save(flags);
mode = READ_ONCE(t->kcov_mode);
barrier();
if (!kcov_mode_enabled(mode)) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
/*
@@ -1017,12 +1014,12 @@ void kcov_remote_stop(void)
* actually found the remote handle and started collecting coverage.
*/
if (in_serving_softirq() && !t->kcov_softirq) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
/* Make sure that kcov_softirq is only set when in softirq. */
if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
return;
}
@@ -1052,7 +1049,7 @@ void kcov_remote_stop(void)
raw_spin_unlock(&kcov_remote_lock);
}
- local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
+ local_irq_restore(flags);
/* Get in kcov_remote_start(). */
kcov_put(kcov);
--
2.50.0
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