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    SubjectRe: [PATCH 5.16 1026/1039] blk-mq: fix tag_get wait task cant be awakened
    On Tue, Jan 25, 2022 at 08:38:01AM +0000, John Garry wrote:
    > On 24/01/2022 18:46, Greg Kroah-Hartman wrote:
    > > From: Laibin Qiu<qiulaibin@huawei.com>
    > >
    > > commit 180dccb0dba4f5e84a4a70c1be1d34cbb6528b32 upstream.
    > >
    > > In case of shared tags, there might be more than one hctx which
    > > allocates from the same tags, and each hctx is limited to allocate at
    > > most:
    > > hctx_max_depth = max((bt->sb.depth + users - 1) / users, 4U);
    > >
    > > tag idle detection is lazy, and may be delayed for 30sec, so there
    > > could be just one real active hctx(queue) but all others are actually
    > > idle and still accounted as active because of the lazy idle detection.
    > > Then if wake_batch is > hctx_max_depth, driver tag allocation may wait
    > > forever on this real active hctx.
    > >
    > > Fix this by recalculating wake_batch when inc or dec active_queues.
    > >
    > > Fixes: 0d2602ca30e41 ("blk-mq: improve support for shared tags maps")
    > > Suggested-by: Ming Lei<ming.lei@redhat.com>
    > > Suggested-by: John Garry<john.garry@huawei.com>
    > > Signed-off-by: Laibin Qiu<qiulaibin@huawei.com>
    > > Reviewed-by: Andy Shevchenko<andriy.shevchenko@linux.intel.com>
    > > Link:https://lore.kernel.org/r/20220113025536.1479653-1-qiulaibin@huawei.com
    > > Signed-off-by: Jens Axboe<axboe@kernel.dk>
    > > Signed-off-by: Greg Kroah-Hartman<gregkh@linuxfoundation.org>
    >
    > JFYI, Somebody reported a hang with this commit:
    > https://lore.kernel.org/linux-block/78cafe94-a787-e006-8851-69906f0c2128@huawei.com/T/#t

    Thanks for the report, I'll go drop this patch now.

    greg k-h

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