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Subject: Re: [PATCH AUTOSEL 4.20 49/77] block: cover another queue enter recursion
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From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To:     Sasha Levin <sashal@kernel.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Ming Lei <ming.lei@redhat.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        NeilBrown <neilb@suse.com>, Jens Axboe <axboe@kernel.dk>,
        Sasha Levin <sashal@kernel.org>, linux-block@vger.kernel.org
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Date:   Fri, 15 Feb 2019 11:24:27 +0900
References: <20190215020855.176727-1-sashal@kernel.org> <20190215020855.176727-49-sashal@kernel.org>
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This patch turned out to be wrong and was reverted. Please drop this patch. 

commit 947b7ac135b16aa60f9141ff72bd494eda0edb5e
Author: Jens Axboe <axboe@kernel.dk>
Date:   Sun Jan 27 06:35:28 2019 -0700

    Revert "block: cover another queue enter recursion via BIO_QUEUE_ENTERED"

    We can't touch a bio after ->make_request_fn(), for all we know it could
    already have been completed by the time this function returns.

    This reverts commit 698cef173983b086977e633e46476e0f925ca01e.

    Reported-by: syzbot+4df6ca820108fd248943@syzkaller.appspotmail.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

> From: Ming Lei <ming.lei@redhat.com>
> 
> [ Upstream commit 698cef173983b086977e633e46476e0f925ca01e ]
> 
> Except for blk_queue_split(), bio_split() is used for splitting bio too,
> then the remained bio is often resubmit to queue via generic_make_request().
> So the same queue enter recursion exits in this case too. Unfortunatley
> commit cd4a4ae4683dc2 doesn't help this case.
> 
> This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
> q->make_request_fn.
> 
> In theory the per-bio flag is used to simulate one stack variable, it is
> just fine to clear it after q->make_request_fn is returned. Especially
> the same bio can't be submitted from another context.
> 
> Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: NeilBrown <neilb@suse.com>
> Reviewed-by:  Mike Snitzer <snitzer@redhat.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  block/blk-core.c  | 11 +++++++++++
>  block/blk-merge.c | 10 ----------
>  2 files changed, 11 insertions(+), 10 deletions(-)