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.
Reviewed-by: Mathieu Desnoyers <[email protected]>
Fixes: 7f184275aa30 ("lib, Make gen_pool memory allocator lockless")
Cc: Andi Kleen <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Riley <[email protected]>
Cc: Eric Miao <[email protected]>
Cc: Grant Likely <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Haojian Zhuang <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Jaroslav Kysela <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Liam Girdwood <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Ritesh Harjain <[email protected]>
Cc: Russell King <[email protected]>
Cc: Sekhar Nori <[email protected]>
Cc: Takashi Iwai <[email protected]>
Cc: Thadeu Lima de Souza Cascardo <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Vinod Koul <[email protected]>
Cc: Vladimir Zapolskiy <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Daniel Mentz <[email protected]>
---
lib/genalloc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/lib/genalloc.c b/lib/genalloc.c
index 0a11396..144fe6b 100644
--- a/lib/genalloc.c
+++ b/lib/genalloc.c
@@ -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;
#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
BUG_ON(in_nmi());
@@ -307,6 +307,7 @@ unsigned long gen_pool_alloc_algo(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 = algo(chunk->bits, end_bit, start_bit,
--
2.8.0.rc3.226.g39d4020
