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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1675111916; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HatpIAXF9ywMATjIlRO5zkwkJoWVcZESn/qWFP01cUE=; b=wXtDfrkYlD8IpL/lQ8l++bN1YdtjxhnwL1anSh49Js2VOzOsVnOBIPbJSklgemF2REahtq DvdvaNag4m/GqwVZu03XHDBsOWpGjVLbIuihC73epl6av328Yy8aLHk/DlbB90DLAwCqg2 4Z44QfKvcXgws9zhTONc9RpzBkBuxac= From: andrey.konovalov@linux.dev To: Marco Elver , Alexander Potapenko Cc: Andrey Konovalov , Vlastimil Babka , kasan-dev@googlegroups.com, Evgenii Stepanov , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrey Konovalov Subject: [PATCH 16/18] lib/stackdepot: annotate racy slab_index accesses Date: Mon, 30 Jan 2023 21:49:40 +0100 Message-Id: <19512bb03eed27ced5abeb5bd03f9a8381742cb1.1675111415.git.andreyknvl@google.com> In-Reply-To: References: MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756482697313529542?= X-GMAIL-MSGID: =?utf-8?q?1756482697313529542?= From: Andrey Konovalov Accesses to slab_index are protected by slab_lock everywhere except in a sanity check in stack_depot_fetch. The read access there can race with the write access in depot_alloc_stack. Use WRITE/READ_ONCE() to annotate the racy accesses. As the sanity check is only used to print a warning in case of a violation of the stack depot interface usage, it does not make a lot of sense to use proper synchronization. Signed-off-by: Andrey Konovalov Signed-off-by: Andrew Morton --- lib/stackdepot.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index f291ad6a4e72..cc2fe8563af4 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -269,8 +269,11 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) return NULL; } - /* Move on to the next slab. */ - slab_index++; + /* + * Move on to the next slab. + * WRITE_ONCE annotates a race with stack_depot_fetch. + */ + WRITE_ONCE(slab_index, slab_index + 1); slab_offset = 0; /* * smp_store_release() here pairs with smp_load_acquire() in @@ -492,6 +495,8 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle, unsigned long **entries) { union handle_parts parts = { .handle = handle }; + /* READ_ONCE annotates a race with depot_alloc_stack. */ + int slab_index_cached = READ_ONCE(slab_index); void *slab; size_t offset = parts.offset << DEPOT_STACK_ALIGN; struct stack_record *stack; @@ -500,9 +505,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle, if (!handle) return 0; - if (parts.slab_index > slab_index) { + if (parts.slab_index > slab_index_cached) { WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n", - parts.slab_index, slab_index, handle); + parts.slab_index, slab_index_cached, handle); return 0; } slab = stack_slabs[parts.slab_index];