| From | Willy Tarreau <> | Subject | [PATCH 3.10 285/319] lib/genalloc.c: start search from start of chunk | Date | Sun, 5 Feb 2017 20:21:47 +0100 |
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From: Daniel Mentz <danielmentz@google.com>
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 <danielmentz@google.com> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> --- lib/genalloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/lib/genalloc.c b/lib/genalloc.c index 2a39bf6..ac5fba9 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, -- 2.8.0.rc2.1.gbe9624a
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