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Subject[PATCH] mm/kasan: make quarantine_lock a raw_spinlock_t
From: Clark Williams <williams@redhat.com>
Date: Tue, 18 Sep 2018 10:29:31 -0500

The static lock quarantine_lock is used in quarantine.c to protect the
quarantine queue datastructures. It is taken inside quarantine queue
manipulation routines (quarantine_put(), quarantine_reduce() and
quarantine_remove_cache()), with IRQs disabled.
This is not a problem on a stock kernel but is problematic on an RT
kernel where spin locks are sleeping spinlocks, which can sleep and can
not be acquired with disabled interrupts.

Convert the quarantine_lock to a raw spinlock_t. The usage of
quarantine_lock is confined to quarantine.c and the work performed while
the lock is held is used for debug purpose.

Signed-off-by: Clark Williams <williams@redhat.com>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[bigeasy: slightly altered the commit message]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
On 2018-10-10 11:57:41 [+0200], Dmitry Vyukov wrote:
> Yes. Clark's patch looks good to me. Probably would be useful to add a
> comment as to why raw spinlock is used (otherwise somebody may
> refactor it back later).

If you really insist, I could add something but this didn't happen so
far. git's changelog should provide enough information why to why it was
changed.

mm/kasan/quarantine.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -103,7 +103,7 @@ static int quarantine_head;
static int quarantine_tail;
/* Total size of all objects in global_quarantine across all batches. */
static unsigned long quarantine_size;
-static DEFINE_SPINLOCK(quarantine_lock);
+static DEFINE_RAW_SPINLOCK(quarantine_lock);
DEFINE_STATIC_SRCU(remove_cache_srcu);

/* Maximum size of the global queue. */
@@ -190,7 +190,7 @@ void quarantine_put(struct kasan_free_me
if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
qlist_move_all(q, &temp);

- spin_lock(&quarantine_lock);
+ raw_spin_lock(&quarantine_lock);
WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
if (global_quarantine[quarantine_tail].bytes >=
@@ -203,7 +203,7 @@ void quarantine_put(struct kasan_free_me
if (new_tail != quarantine_head)
quarantine_tail = new_tail;
}
- spin_unlock(&quarantine_lock);
+ raw_spin_unlock(&quarantine_lock);
}

local_irq_restore(flags);
@@ -230,7 +230,7 @@ void quarantine_reduce(void)
* expected case).
*/
srcu_idx = srcu_read_lock(&remove_cache_srcu);
- spin_lock_irqsave(&quarantine_lock, flags);
+ raw_spin_lock_irqsave(&quarantine_lock, flags);

/*
* Update quarantine size in case of hotplug. Allocate a fraction of
@@ -254,7 +254,7 @@ void quarantine_reduce(void)
quarantine_head = 0;
}

- spin_unlock_irqrestore(&quarantine_lock, flags);
+ raw_spin_unlock_irqrestore(&quarantine_lock, flags);

qlist_free_all(&to_free, NULL);
srcu_read_unlock(&remove_cache_srcu, srcu_idx);
@@ -310,17 +310,17 @@ void quarantine_remove_cache(struct kmem
*/
on_each_cpu(per_cpu_remove_cache, cache, 1);

- spin_lock_irqsave(&quarantine_lock, flags);
+ raw_spin_lock_irqsave(&quarantine_lock, flags);
for (i = 0; i < QUARANTINE_BATCHES; i++) {
if (qlist_empty(&global_quarantine[i]))
continue;
qlist_move_cache(&global_quarantine[i], &to_free, cache);
/* Scanning whole quarantine can take a while. */
- spin_unlock_irqrestore(&quarantine_lock, flags);
+ raw_spin_unlock_irqrestore(&quarantine_lock, flags);
cond_resched();
- spin_lock_irqsave(&quarantine_lock, flags);
+ raw_spin_lock_irqsave(&quarantine_lock, flags);
}
- spin_unlock_irqrestore(&quarantine_lock, flags);
+ raw_spin_unlock_irqrestore(&quarantine_lock, flags);

qlist_free_all(&to_free, cache);

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