The default max_cache_size_bytes for dm-bufio is meant to be the lesser
of 25% of the size of the vmalloc area and 2% of the size of lowmem.
However, on 32-bit systems the intermediate result in the expression
(VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100
overflows, causing the wrong result to be computed. For example, on a
32-bit system where the vmalloc area is 520093696 bytes, the result is
1174405 rather than the expected 130023424, which makes the maximum
cache size much too small (far less than 2% of lowmem). This causes
severe performance problems for dm-verity users on affected systems.
Fix this by using mult_frac() to correctly multiply by a percentage. Do
this for all places in dm-bufio that multiply by a percentage. Also
replace (VMALLOC_END - VMALLOC_START) with VMALLOC_TOTAL, which contrary
to the comment is now defined in include/linux/vmalloc.h.
Fixes: 95d402f057f2 ("dm: add bufio")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.2+
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
drivers/md/dm-bufio.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 33bb074d6941..b8ac591aaaa7 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -974,7 +974,8 @@ static void __get_memory_limit(struct dm_bufio_client *c,
buffers = c->minimum_buffers;
*limit_buffers = buffers;
- *threshold_buffers = buffers * DM_BUFIO_WRITEBACK_PERCENT / 100;
+ *threshold_buffers = mult_frac(buffers,
+ DM_BUFIO_WRITEBACK_PERCENT, 100);
}
/*
@@ -1910,19 +1911,15 @@ static int __init dm_bufio_init(void)
memset(&dm_bufio_caches, 0, sizeof dm_bufio_caches);
memset(&dm_bufio_cache_names, 0, sizeof dm_bufio_cache_names);
- mem = (__u64)((totalram_pages - totalhigh_pages) *
- DM_BUFIO_MEMORY_PERCENT / 100) << PAGE_SHIFT;
+ mem = (__u64)mult_frac(totalram_pages - totalhigh_pages,
+ DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;
if (mem > ULONG_MAX)
mem = ULONG_MAX;
#ifdef CONFIG_MMU
- /*
- * Get the size of vmalloc space the same way as VMALLOC_TOTAL
- * in fs/proc/internal.h
- */
- if (mem > (VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100)
- mem = (VMALLOC_END - VMALLOC_START) * DM_BUFIO_VMALLOC_PERCENT / 100;
+ if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
+ mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
#endif
dm_bufio_default_cache_size = mem;
--
2.15.0.448.gf294e3d99a-goog