On Wed, Aug 31, 2016 at 03:03:24PM -0700, Bart Van Assche wrote: > Protect sw-ctx busy bit manipulations via the sw queue lock. > This allows to convert the atomic bit operations into slightly > faster non-atomic operations. Document that blk_mq_run_hw_queues() > tests these bits without holding the sw queue lock. > > Signed-off-by: Bart Van Assche <[email protected]> > Cc: Christoph Hellwig <[email protected]> > Cc: Sagi Grimberg <[email protected]> > --- > block/blk-mq.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 13f5a6c..0dcafa6 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -66,8 +66,9 @@ static void blk_mq_hctx_mark_pending(struct blk_mq_hw_ctx > *hctx, > { > struct blk_align_bitmap *bm = get_bm(hctx, ctx); > > + lockdep_assert_held(&ctx->lock); > if (!test_bit(CTX_TO_BIT(hctx, ctx), &bm->word)) > - set_bit(CTX_TO_BIT(hctx, ctx), &bm->word); > + __set_bit(CTX_TO_BIT(hctx, ctx), &bm->word); > } > > static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx, > @@ -75,7 +76,8 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx > *hctx, > { > struct blk_align_bitmap *bm = get_bm(hctx, ctx); > > - clear_bit(CTX_TO_BIT(hctx, ctx), &bm->word); > + lockdep_assert_held(&ctx->lock); > + __clear_bit(CTX_TO_BIT(hctx, ctx), &bm->word); > }
NAK, we can't protect each bit with a separate lock, multiple software queues share the bitmap. There's a race if we do non-atomic bit operations on two software queues with bits in the same word. -- Omar -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
