Commit 62e931fa authored by Daniel Mentz's avatar Daniel Mentz Committed by Linus Torvalds

lib/genalloc.c: start search from start of chunk

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))

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: 7f184275 ("lib, Make gen_pool memory allocator lockless")
Link: default avatarDaniel Mentz <>
Reviewed-by: default avatarMathieu Desnoyers <>
Acked-by: default avatarWill Deacon <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 89a28483
......@@ -292,7 +292,7 @@ unsigned long gen_pool_alloc_algo(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;
......@@ -307,6 +307,7 @@ unsigned long gen_pool_alloc_algo(struct gen_pool *pool, size_t size,
if (size > atomic_read(&chunk->avail))
start_bit = 0;
end_bit = chunk_size(chunk) >> order;
start_bit = algo(chunk->bits, end_bit, start_bit,
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