Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754330AbcKYI5P (ORCPT ); Fri, 25 Nov 2016 03:57:15 -0500 Received: from mx2.suse.de ([195.135.220.15]:45259 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753024AbcKYIbq (ORCPT ); Fri, 25 Nov 2016 03:31:46 -0500 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Daniel Mentz , Andrew Morton , Linus Torvalds , Jiri Slaby Subject: [PATCH 3.12 064/127] lib/genalloc.c: start search from start of chunk Date: Fri, 25 Nov 2016 09:29:37 +0100 Message-Id: <43aa0aa5757342a668fdff5a171bad631ba564c3.1480062521.git.jslaby@suse.cz> X-Mailer: git-send-email 2.10.2 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2695 Lines: 71 From: Daniel Mentz 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 62e931fac45b17c2a42549389879411572f75804 upstream. gen_pool_alloc_algo() iterates over the chunks of a pool trying to find a contiguous block of memory that satisfies the allocation request. The shortcut if (size > atomic_read(&chunk->avail)) continue; makes the loop skip over chunks that do not have enough bytes left to fulfill the request. There are two situations, though, where an allocation might still fail: (1) The available memory is not contiguous, i.e. the request cannot be fulfilled due to external fragmentation. (2) A race condition. Another thread runs the same code concurrently and is quicker to grab the available memory. In those situations, the loop calls pool->algo() to search the entire chunk, and pool->algo() returns some value that is >= end_bit to indicate that the search failed. This return value is then assigned to start_bit. The variables start_bit and end_bit describe the range that should be searched, and this range should be reset for every chunk that is searched. Today, the code fails to reset start_bit to 0. As a result, prefixes of subsequent chunks are ignored. Memory allocations might fail even though there is plenty of room left in these prefixes of those other chunks. Fixes: 7f184275aa30 ("lib, Make gen_pool memory allocator lockless") Link: http://lkml.kernel.org/r/1477420604-28918-1-git-send-email-danielmentz@google.com Signed-off-by: Daniel Mentz Reviewed-by: Mathieu Desnoyers Acked-by: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Jiri Slaby --- lib/genalloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/genalloc.c b/lib/genalloc.c index 26cf20be72b7..17271ef368ca 100644 --- a/lib/genalloc.c +++ b/lib/genalloc.c @@ -273,7 +273,7 @@ unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size) struct gen_pool_chunk *chunk; unsigned long addr = 0; int order = pool->min_alloc_order; - int nbits, start_bit = 0, end_bit, remain; + int nbits, start_bit, end_bit, remain; #ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG BUG_ON(in_nmi()); @@ -288,6 +288,7 @@ unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size) if (size > atomic_read(&chunk->avail)) continue; + start_bit = 0; end_bit = chunk_size(chunk) >> order; retry: start_bit = pool->algo(chunk->bits, end_bit, start_bit, nbits, -- 2.10.2