lib: stackdepot: turn depot_lock spinlock to raw_spinlock

In RT system, the spin_lock will be replaced by sleepable rt_mutex lock,
in __call_rcu(), disable interrupts before calling
kasan_record_aux_stack(), will trigger this calltrace:

  BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:951
  in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 19, name: pgdatinit0
  Call Trace:
    ___might_sleep.cold+0x1b2/0x1f1
    rt_spin_lock+0x3b/0xb0
    stack_depot_save+0x1b9/0x440
    kasan_save_stack+0x32/0x40
    kasan_record_aux_stack+0xa5/0xb0
    __call_rcu+0x117/0x880
    __exit_signal+0xafb/0x1180
    release_task+0x1d6/0x480
    exit_notify+0x303/0x750
    do_exit+0x678/0xcf0
    kthread+0x364/0x4f0
    ret_from_fork+0x22/0x30

Replace spinlock with raw_spinlock.

Link: https://lkml.kernel.org/r/20210329084009.27013-1-qiang.zhang@windriver.com
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Reported-by: Andrew Halaney <ahalaney@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Vinayak Menon <vinmenon@codeaurora.org>
Cc: Yogesh Lal <ylal@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/stackdepot.c

@@ -71,7 +71,7 @@ static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
 static int depot_index;
 static int next_slab_inited;
 static size_t depot_offset;
-static DEFINE_SPINLOCK(depot_lock);
+static DEFINE_RAW_SPINLOCK(depot_lock);
 
 static bool init_stack_slab(void **prealloc)
 {
@@ -305,7 +305,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 			prealloc = page_address(page);
 	}
 
-	spin_lock_irqsave(&depot_lock, flags);
+	raw_spin_lock_irqsave(&depot_lock, flags);
 
 	found = find_stack(*bucket, entries, nr_entries, hash);
 	if (!found) {
@@ -329,7 +329,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 		WARN_ON(!init_stack_slab(&prealloc));
 	}
 
-	spin_unlock_irqrestore(&depot_lock, flags);
+	raw_spin_unlock_irqrestore(&depot_lock, flags);
 exit:
 	if (prealloc) {
 		/* Nobody used this memory, ok to free it. */