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drbd: bitmap: don't count unused bits (fix non-terminating resync) 

We trusted the on-disk bitmap to have unused bits cleared.
In case that is not true for whatever reason,
and we take a code path where the unused bits don't get cleared
elsewhere (bm_clear_surplus is not called), we may miscount the bits,
and get confused during resync, waiting for bits to get cleared that we
don't even use: the resync process would not terminate.

Fix this by masking out unused bits in __bm_count_bits.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
This commit is contained in:
Lars Ellenberg 2010-12-15 23:21:39 +01:00 committed by Philipp Reisner
parent 1b881ef775
commit 7777a8ba1f
1 changed files with 22 additions and 3 deletions
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25
drivers/block/drbd/drbd_bitmap.c
View File

@ -376,9 +376,16 @@ static unsigned long __bm_count_bits(struct drbd_bitmap *b, const int swap_endia
unsigned long *p_addr, *bm, offset = 0;
unsigned long bits = 0;
unsigned long i, do_now;
unsigned long words;
while (offset < b->bm_words) {
i = do_now = min_t(size_t, b->bm_words-offset, LWPP);
/* due to 64bit alignment, the last long on a 32bit arch
* may be not used at all. The last used long will likely
* be only partially used, always. Don't count those bits,
* but mask them out. */
words = (b->bm_bits + BITS_PER_LONG - 1) >> LN2_BPL;
while (offset < words) {
i = do_now = min_t(size_t, words-offset, LWPP);
p_addr = __bm_map_paddr(b, offset, KM_USER0);
bm = p_addr + MLPP(offset);
while (i--) {
@ -388,8 +395,20 @@ static unsigned long __bm_count_bits(struct drbd_bitmap *b, const int swap_endia
#endif
bits += hweight_long(*bm++);
}
__bm_unmap(p_addr, KM_USER0);
offset += do_now;
if (offset == words) {
/* last word may only be partially used,
* see also bm_clear_surplus. */
i = (1UL << (b->bm_bits & (BITS_PER_LONG-1))) -1;
if (i) {
bits -= hweight_long(p_addr[do_now-1] & ~i);
p_addr[do_now-1] &= i;
}
/* 32bit arch, may have an unused padding long */
if (words != b->bm_words)
p_addr[do_now] = 0;
}
__bm_unmap(p_addr, KM_USER0);
cond_resched();
}