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@kzalloc.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);