+ lib-genallocc-start-search-from-start-of-chunk.patch added to -mm tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: lib/genalloc.c: start search from start of chunk
has been added to the -mm tree.  Its filename is
     lib-genallocc-start-search-from-start-of-chunk.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/lib-genallocc-start-search-from-start-of-chunk.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/lib-genallocc-start-search-from-start-of-chunk.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
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>
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,
_

Patches currently in -mm which might be from danielmentz@xxxxxxxxxx are

lib-genallocc-start-search-from-start-of-chunk.patch

--
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



[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]
  Powered by Linux