Commit e124670f authored Sep 17, 2019 by Jim Shu Committed by Anas Nashif Sep 26, 2019

kernel/spinlock: Fix a SMP race condition of SPIN_VALIDATE



z_spin_lock_valid() reads shared variable twice to do two checkings. If
this variable is modified by other CPU between two read accesses, the
checking value is inconsistent. This inconsistency causes the error
that CPU0 can pass the checking when it doesn't hold spinlock because
zeroed-out thread_cpu value is ambiguous with the CPU0 ID.

Fix the inconsistency by only reading shared variable once and using
local variable value to do two checkings.

Fixes #19299.

Signed-off-by: Jim Shu <cwshu@andestech.com>

parent 14c200d0

kernel/thread.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -805,8 +805,10 @@ FUNC_NORETURN void k_thread_user_mode_enter(k_thread_entry_t entry,
		#ifdef SPIN_VALIDATE
		bool z_spin_lock_valid(struct k_spinlock *l)
		{
		if (l->thread_cpu) {
		if ((l->thread_cpu & 3) == _current_cpu->id) {
		uintptr_t thread_cpu = l->thread_cpu;

		if (thread_cpu) {
		if ((thread_cpu & 3) == _current_cpu->id) {
		return false;
		}
		}

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