Messages in this thread | | | Date | Wed, 18 Mar 2015 14:40:08 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH] blkmq: Fix NULL pointer deref when all reserved tags in use |
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On 03/18/2015 02:36 PM, Sam Bradshaw wrote: > When allocating from the reserved tags pool, bt_get() is called with > a NULL hctx. If all tags are in use, the hw queue is kicked to push > out any pending IO, potentially freeing tags, and tag allocation is > retried. The problem is that blk_mq_run_hw_queue() doesn't check for > a NULL hctx. This patch fixes that bug. > > An alternative implementation might skip kicking the queue for reserved > tags and go right to io_schedule() but we chose to keep it simple. > > Tested by hammering mtip32xx with concurrent smartctl/hdparm. > > Signed-off-by: Sam Bradshaw <sbradshaw@micron.com> > Signed-off-by: Selvan Mani <smani@micron.com> > --- > block/blk-mq.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 59fa239..0471af6 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -887,7 +887,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) > > void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) > { > - if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state) || > + if (unlikely(!hctx || test_bit(BLK_MQ_S_STOPPED, &hctx->state) || > !blk_mq_hw_queue_mapped(hctx))) > return;
Good catch! But why not put the hctx == NULL check in as a conditional in bt_get() before running the queue? I can't imagine other cases where calling blk_mq_run_hw_queue() with hctx == NULL would be a valid scenario.
The bug was introduced with commit b32232073e80, so that should probably be indicated too.
-- Jens Axboe
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