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Commit b41f4d4a authored by Sami Tolvanen's avatar Sami Tolvanen
Browse files

ANDROID: scs: fix recursive spinlock in scs_check_usage 



Use cmpxchg instead of a spinlock in scs_check_usage() to avoid
deadlocks.

Bug: 157781894
Change-Id: I1701ccaf25fdbd34ce4798c6f93e220b1565fb34
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
parent 3045070c

kernel/scs.c

+17 −22
Original line number Diff line number Diff line
@@ -185,36 +185,31 @@ int scs_prepare(struct task_struct *tsk, int node) 
}



#ifdef CONFIG_DEBUG_STACK_USAGE

static inline unsigned long scs_used(struct task_struct *tsk)

static void scs_check_usage(struct task_struct *tsk)

{

	static unsigned long highest;



	unsigned long *p = __scs_base(tsk);

	unsigned long *end = scs_magic(p);

	unsigned long s = (unsigned long)p;

	unsigned long prev, curr = highest, used = 0;



	while (p < end && READ_ONCE_NOCHECK(*p))

		p++;



	return (unsigned long)p - s;

	for (; p < end; ++p) {

		if (!READ_ONCE_NOCHECK(*p))

			break;

		used += sizeof(*p);

	}



static void scs_check_usage(struct task_struct *tsk)

{

	static DEFINE_SPINLOCK(lock);

	static unsigned long highest;

	unsigned long used = scs_used(tsk);



	if (used <= highest)

		return;

	while (used > curr) {

		prev = cmpxchg_relaxed(&highest, curr, used);



	spin_lock(&lock);



	if (used > highest) {

		if (prev == curr) {

			pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",

				tsk->comm, task_pid_nr(tsk), used);

		highest = used;

			break;

		}



	spin_unlock(&lock);

		curr = prev;

	}

}

#else

static inline void scs_check_usage(struct task_struct *tsk)