From:   andrey.konovalov@linux.dev
To:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        Evgenii Stepanov <eugenis@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH 13/18] lib/stacktrace: drop impossible WARN_ON for depot_init_slab
Date:   Mon, 30 Jan 2023 21:49:37 +0100
Message-Id: <7e7434a0d4e8a71138aec2c8a3c69a4eebf49935.1675111415.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

depot_init_slab has two call sites:

1. In depot_alloc_stack with a potentially NULL prealloc.
2. In __stack_depot_save with a non-NULL prealloc.

At the same time depot_init_slab can only return false when prealloc is
NULL.

As the second call site makes sure that prealloc is not NULL, the WARN_ON
there can never trigger. Thus, drop the WARN_ON and also move the prealloc
check from depot_init_slab to its first call site.

Also change the return type of depot_init_slab to void as it now always
returns true.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/stackdepot.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index b946ba74fea0..d6be82a5c223 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -218,16 +218,14 @@ int stack_depot_init(void)
 }
 EXPORT_SYMBOL_GPL(stack_depot_init);
 
-static bool depot_init_slab(void **prealloc)
+static void depot_init_slab(void **prealloc)
 {
-	if (!*prealloc)
-		return false;
 	/*
 	 * This smp_load_acquire() pairs with smp_store_release() to
 	 * |next_slab_inited| below and in depot_alloc_stack().
 	 */
 	if (smp_load_acquire(&next_slab_inited))
-		return true;
+		return;
 	if (stack_slabs[slab_index] == NULL) {
 		stack_slabs[slab_index] = *prealloc;
 		*prealloc = NULL;
@@ -244,7 +242,6 @@ static bool depot_init_slab(void **prealloc)
 			smp_store_release(&next_slab_inited, 1);
 		}
 	}
-	return true;
 }
 
 /* Allocation of a new stack in raw storage */
@@ -271,7 +268,8 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 		if (slab_index + 1 < DEPOT_MAX_SLABS)
 			smp_store_release(&next_slab_inited, 0);
 	}
-	depot_init_slab(prealloc);
+	if (*prealloc)
+		depot_init_slab(prealloc);
 	if (stack_slabs[slab_index] == NULL)
 		return NULL;
 
@@ -436,7 +434,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		 * We didn't need to store this stack trace, but let's keep
 		 * the preallocated memory for the future.
 		 */
-		WARN_ON(!depot_init_slab(&prealloc));
+		depot_init_slab(&prealloc);
 	}
 
 	raw_spin_unlock_irqrestore(&slab_lock, flags);
-- 
2.25.1