From: Neil Brown Date: Thu, 8 Feb 2007 22:20:37 +0000 (-0800) Subject: [PATCH] md: avoid possible BUG_ON in md bitmap handling X-Git-Tag: v2.6.21-rc1~83^2~19 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=da6e1a32fb8d7539a27f699c8671f64d7fefd0cc;p=linux-2.6-omap-h63xx.git [PATCH] md: avoid possible BUG_ON in md bitmap handling md/bitmap tracks how many active write requests are pending on blocks associated with each bit in the bitmap, so that it knows when it can clear the bit (when count hits zero). The counter has 14 bits of space, so if there are ever more than 16383, we cannot cope. Currently the code just calles BUG_ON as "all" drivers have request queue limits much smaller than this. However is seems that some don't. Apparently some multipath configurations can allow more than 16383 concurrent write requests. So, in this unlikely situation, instead of calling BUG_ON we now wait for the count to drop down a bit. This requires a new wait_queue_head, some waiting code, and a wakeup call. Tested by limiting the counter to 20 instead of 16383 (writes go a lot slower in that case...). Signed-off-by: Neil Brown Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c index 11108165e26..059704fbb75 100644 --- a/drivers/md/bitmap.c +++ b/drivers/md/bitmap.c @@ -1160,6 +1160,22 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect return 0; } + if (unlikely((*bmc & COUNTER_MAX) == COUNTER_MAX)) { + DEFINE_WAIT(__wait); + /* note that it is safe to do the prepare_to_wait + * after the test as long as we do it before dropping + * the spinlock. + */ + prepare_to_wait(&bitmap->overflow_wait, &__wait, + TASK_UNINTERRUPTIBLE); + spin_unlock_irq(&bitmap->lock); + bitmap->mddev->queue + ->unplug_fn(bitmap->mddev->queue); + schedule(); + finish_wait(&bitmap->overflow_wait, &__wait); + continue; + } + switch(*bmc) { case 0: bitmap_file_set_bit(bitmap, offset); @@ -1169,7 +1185,7 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect case 1: *bmc = 2; } - BUG_ON((*bmc & COUNTER_MAX) == COUNTER_MAX); + (*bmc)++; spin_unlock_irq(&bitmap->lock); @@ -1207,6 +1223,9 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto if (!success && ! (*bmc & NEEDED_MASK)) *bmc |= NEEDED_MASK; + if ((*bmc & COUNTER_MAX) == COUNTER_MAX) + wake_up(&bitmap->overflow_wait); + (*bmc)--; if (*bmc <= 2) { set_page_attr(bitmap, @@ -1431,6 +1450,7 @@ int bitmap_create(mddev_t *mddev) spin_lock_init(&bitmap->lock); atomic_set(&bitmap->pending_writes, 0); init_waitqueue_head(&bitmap->write_wait); + init_waitqueue_head(&bitmap->overflow_wait); bitmap->mddev = mddev; diff --git a/include/linux/raid/bitmap.h b/include/linux/raid/bitmap.h index ebd42a3710b..6db9a4c1535 100644 --- a/include/linux/raid/bitmap.h +++ b/include/linux/raid/bitmap.h @@ -247,6 +247,7 @@ struct bitmap { atomic_t pending_writes; /* pending writes to the bitmap file */ wait_queue_head_t write_wait; + wait_queue_head_t overflow_wait; };