On Tue, 2018-04-10 at 20:10 -0600, Jens Axboe wrote:
> On 4/10/18 8:05 PM, Ming Lei wrote:
> > On Tue, Apr 10, 2018 at 02:30:35PM -0600, Bart Van Assche wrote:
> > > Because blkcg_exit_queue() is now called from inside blk_cleanup_queue()
> > > it is no longer safe to access cgroup information during or after the
> > > blk_cleanup_queue() call. Hence protect the generic_make_request_checks()
> > > call with blk_queue_enter() / blk_queue_exit().
> > >
> > > Reported-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > > Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the block cgroup controller")
> > > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> > > Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> > > Cc: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> > > ---
> > > block/blk-core.c | 32 ++++++++++++++++++++++++++------
> > > 1 file changed, 26 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/block/blk-core.c b/block/blk-core.c
> > > index 34e2f2227fd9..a330cd2829e1 100644
> > > --- a/block/blk-core.c
> > > +++ b/block/blk-core.c
> > > @@ -2386,8 +2386,19 @@ blk_qc_t generic_make_request(struct bio *bio)
> > > * yet.
> > > */
> > > struct bio_list bio_list_on_stack[2];
> > > + blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
> > > + BLK_MQ_REQ_NOWAIT : 0;
> > > + struct request_queue *q = bio->bi_disk->queue;
> > > blk_qc_t ret = BLK_QC_T_NONE;
> > >
> > > + if (blk_queue_enter(q, flags) < 0) {
> >
> > As I mentioned last time, the queue pointer has to be checked before
> > calling blk_queue_enter(), since it isn't difficult to trigger the
> > failure log of 'generic_make_request: Trying to access nonexistent
> > block-device'.
>
> That's a good point, the NULL check needs to be included first. Bart,
> do you want to send an update? I can just rebase the for-linus branch.
But how could the request pointer be NULL? Which code clears that pointer?
Thanks,
Bart.
