From: Daniel Mentz <danielmentz@xxxxxxxxxx>
Subject: 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))
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@xxxxxxxxxx
Signed-off-by: Daniel Mentz <danielmentz@xxxxxxxxxx>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/genalloc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN lib/genalloc.c~lib-genallocc-start-search-from-start-of-chunk lib/genalloc.c
--- a/lib/genalloc.c~lib-genallocc-start-search-from-start-of-chunk
+++ a/lib/genalloc.c
@@ -292,7 +292,7 @@ unsigned long gen_pool_alloc_algo(struct
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
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,
_
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
