On Tue, Sep 29, 2015 at 08:41:31PM -0400, Dan Williams wrote:
> Allow pmem, and other synchronous/bio-based block drivers, to fallback
> on a per-cpu reference count managed by the core for tracking queue
> live/dead state.
>
> The existing per-cpu reference count for the blk_mq case is promoted to
> be used in all block i/o scenarios. This involves initializing it by
> default, waiting for it to drop to zero at exit, and holding a live
> reference over the invocation of q->make_request_fn() in
> generic_make_request(). The blk_mq code continues to take its own
> reference per blk_mq request and retains the ability to freeze the
> queue, but the check that the queue is frozen is moved to
> generic_make_request().
>
> This fixes crash signatures like the following:
>
> BUG: unable to handle kernel paging request at ffff880140000000
> [..]
> Call Trace:
> [<ffffffff8145e8bf>] ? copy_user_handle_tail+0x5f/0x70
> [<ffffffffa004e1e0>] pmem_do_bvec.isra.11+0x70/0xf0 [nd_pmem]
> [<ffffffffa004e331>] pmem_make_request+0xd1/0x200 [nd_pmem]
> [<ffffffff811c3162>] ? mempool_alloc+0x72/0x1a0
> [<ffffffff8141f8b6>] generic_make_request+0xd6/0x110
> [<ffffffff8141f966>] submit_bio+0x76/0x170
> [<ffffffff81286dff>] submit_bh_wbc+0x12f/0x160
> [<ffffffff81286e62>] submit_bh+0x12/0x20
> [<ffffffff813395bd>] jbd2_write_superblock+0x8d/0x170
> [<ffffffff8133974d>] jbd2_mark_journal_empty+0x5d/0x90
> [<ffffffff813399cb>] jbd2_journal_destroy+0x24b/0x270
> [<ffffffff810bc4ca>] ? put_pwq_unlocked+0x2a/0x30
> [<ffffffff810bc6f5>] ? destroy_workqueue+0x225/0x250
> [<ffffffff81303494>] ext4_put_super+0x64/0x360
> [<ffffffff8124ab1a>] generic_shutdown_super+0x6a/0xf0
>
> Cc: Jens Axboe <ax...@kernel.dk>
> Cc: Keith Busch <keith.bu...@intel.com>
> Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
> Suggested-by: Christoph Hellwig <h...@lst.de>
> Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
> ---
> block/blk-core.c | 71 +++++++++++++++++++++++++++++++++++++------
> block/blk-mq-sysfs.c | 6 ----
> block/blk-mq.c | 80
> ++++++++++++++----------------------------------
> block/blk-sysfs.c | 3 +-
> block/blk.h | 14 ++++++++
> include/linux/blk-mq.h | 1 -
> include/linux/blkdev.h | 2 +
> 7 files changed, 102 insertions(+), 75 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 2eb722d48773..6062550baaef 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -554,19 +554,17 @@ void blk_cleanup_queue(struct request_queue *q)
> * Drain all requests queued before DYING marking. Set DEAD flag to
> * prevent that q->request_fn() gets invoked after draining finished.
> */
> - if (q->mq_ops) {
> - blk_mq_freeze_queue(q);
> - spin_lock_irq(lock);
> - } else {
> - spin_lock_irq(lock);
> + blk_freeze_queue(q);
> + spin_lock_irq(lock);
> + if (!q->mq_ops)
> __blk_drain_queue(q, true);
> - }
__blk_drain_queue really ought to be moved into blk_freeze_queue so it
has equivlaent functionality for mq vs !mq. But maybe that can be a
separate patch.
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