3.2.99-rc1 review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit 74d4108d9e681dbbe4a2940ed8fdff1f6868184c upstream.
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.
Depends-on: 9993bc635 ("sched/x86: Fix overflow in cyc2ns_offset") Fixes: 95d402f057f2 ("dm: add bufio") Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Mike Snitzer snitzer@redhat.com [bwh: Backported to 3.2: keep open-coded VMALLOC_TOTAL] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/md/dm-bufio.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)
--- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -839,7 +839,8 @@ static void __get_memory_limit(struct dm buffers = DM_BUFIO_MIN_BUFFERS;
*limit_buffers = buffers; - *threshold_buffers = buffers * DM_BUFIO_WRITEBACK_PERCENT / 100; + *threshold_buffers = mult_frac(buffers, + DM_BUFIO_WRITEBACK_PERCENT, 100); }
/* @@ -1620,19 +1621,15 @@ 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_END - VMALLOC_START, DM_BUFIO_VMALLOC_PERCENT, 100)) + mem = mult_frac(VMALLOC_END - VMALLOC_START, DM_BUFIO_VMALLOC_PERCENT, 100); #endif
dm_bufio_default_cache_size = mem;