From: Neil Brown 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 Signed-off-by: Greg Kroah-Hartman diff .prev/drivers/md/bitmap.c ./drivers/md/bitmap.c --- drivers/md/bitmap.c | 22 +++++++++++++++++++++- include/linux/raid/bitmap.h | 1 + 2 files changed, 22 insertions(+), 1 deletion(-) --- linux-2.6.20.1.orig/drivers/md/bitmap.c +++ linux-2.6.20.1/drivers/md/bitmap.c @@ -1160,6 +1160,22 @@ int bitmap_startwrite(struct bitmap *bit 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 *bit 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 *bitm 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; --- linux-2.6.20.1.orig/include/linux/raid/bitmap.h +++ linux-2.6.20.1/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; }; -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/