From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: [PATCH -stable] block: destroy bdi before blockdev is unregistered. Date: Wed, 29 Apr 2015 07:25:30 +1000 Message-ID: <20150429072530.39d38b00@notabene.brown> References: <20150414171537.GH25394@azat> <20150423160551.45345f96@notabene.brown> <20150427141222.5dac22f1@notabene.brown> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/a/y=o1PKzbldPLSytCnnabX"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mike Snitzer Cc: Jens Axboe , Azat Khuzhin , Christoph Hellwig , "Kernel.org-Linux-RAID" , Guoqing Jiang , Tejun Heo , Jan Kara , lkml , device-mapper development List-Id: linux-raid.ids --Sig_/a/y=o1PKzbldPLSytCnnabX Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Tue, 28 Apr 2015 12:41:18 -0400 Mike Snitzer wrote: > On Mon, Apr 27, 2015 at 12:12 AM, NeilBrown wrote: > > > > Because of the peculiar way that md devices are created (automatically > > when the device node is opened), a new device can be created and > > registered immediately after the > > blk_unregister_region(disk_devt(disk), disk->minors); > > call in del_gendisk(). > > > > Therefore it is important that all visible artifacts of the previous > > device are removed before this call. In particular, the 'bdi'. > > > > Since: > > commit c4db59d31e39ea067c32163ac961e9c80198fd37 > > Author: Christoph Hellwig > > fs: don't reassign dirty inodes to default_backing_dev_info > > > > moved the > > device_unregister(bdi->dev); > > call from bdi_unregister() to bdi_destroy() it has been quite easy to > > lose a race and have a new (e.g.) "md127" be created after the > > blk_unregister_region() call and before bdi_destroy() is ultimately > > called by the final 'put_disk', which must come after del_gendisk(). > > > > The new device finds that the bdi name is already registered in sysfs > > and complains > > > >> [ 9627.630029] WARNING: CPU: 18 PID: 3330 at fs/sysfs/dir.c:31 sysfs_w= arn_dup+0x5a/0x70() > >> [ 9627.630032] sysfs: cannot create duplicate filename '/devices/virtu= al/bdi/9:127' > > > > We can fix this by moving the bdi_destroy() call out of > > blk_release_queue() (which can happen very late when a refcount > > reaches zero) and into blk_cleanup_queue() - which happens exactly when= the md > > device driver calls it. > > > > Then it is only necessary for md to call blk_cleanup_queue() before > > del_gendisk(). As loop.c devices are also created on demand by > > opening the device node, we make the same change there. > > > > Fixes: c4db59d31e39ea067c32163ac961e9c80198fd37 > > Reported-by: Azat Khuzhin > > Cc: Christoph Hellwig > > Cc: stable@vger.kernel.org (v4.0) > > Signed-off-by: NeilBrown > > > > -- > > Hi Jens, > > if you could check this and forward on to Linus I'd really appreciate = it. > > > > Thanks, > > NeilBrown > > > > > > diff --git a/block/blk-core.c b/block/blk-core.c > > index fd154b94447a..7871603f0a29 100644 > > --- a/block/blk-core.c > > +++ b/block/blk-core.c > > @@ -552,6 +552,8 @@ void blk_cleanup_queue(struct request_queue *q) > > q->queue_lock =3D &q->__queue_lock; > > spin_unlock_irq(lock); > > > > + bdi_destroy(&q->backing_dev_info); > > + > > /* @q is and will stay empty, shutdown and put */ > > blk_put_queue(q); > > } > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > > index faaf36ade7eb..2b8fd302f677 100644 > > --- a/block/blk-sysfs.c > > +++ b/block/blk-sysfs.c > > @@ -522,8 +522,6 @@ static void blk_release_queue(struct kobject *kobj) > > > > blk_trace_shutdown(q); > > > > - bdi_destroy(&q->backing_dev_info); > > - > > ida_simple_remove(&blk_queue_ida, q->id); > > call_rcu(&q->rcu_head, blk_free_queue_rcu); > > } > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > > index ae3fcb4199e9..d7173cb1ea76 100644 > > --- a/drivers/block/loop.c > > +++ b/drivers/block/loop.c > > @@ -1620,8 +1620,8 @@ out: > > > > static void loop_remove(struct loop_device *lo) > > { > > - del_gendisk(lo->lo_disk); > > blk_cleanup_queue(lo->lo_queue); > > + del_gendisk(lo->lo_disk); > > blk_mq_free_tag_set(&lo->tag_set); > > put_disk(lo->lo_disk); > > kfree(lo); > > diff --git a/drivers/md/md.c b/drivers/md/md.c > > index d4f31e195e26..593a02476c78 100644 > > --- a/drivers/md/md.c > > +++ b/drivers/md/md.c > > @@ -4818,12 +4818,12 @@ static void md_free(struct kobject *ko) > > if (mddev->sysfs_state) > > sysfs_put(mddev->sysfs_state); > > > > + if (mddev->queue) > > + blk_cleanup_queue(mddev->queue); > > if (mddev->gendisk) { > > del_gendisk(mddev->gendisk); > > put_disk(mddev->gendisk); > > } > > - if (mddev->queue) > > - blk_cleanup_queue(mddev->queue); > > > > kfree(mddev); > > } >=20 > I've taken this patch into consideration relative to DM, please see: > http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h= =3Dwip&id=3D5dac86fb79697e93297edb6a316b429236d00137 >=20 > Point is in my private snitzer/wip branch DM now calls > blk_cleanup_queue() before del_gendisk(). >=20 > With your patch: > 1) blk_cleanup_queue -> bdi_destroy -> bdi->dev =3D NULL; > 2) del_gendisk -> bdi_unregister -> WARN_ON_ONCE(!bdi->dev) >=20 > So, in testing with DM I'm hitting bdi_unregister's WARN_ON(), are you > seeing this WARN_ON? Hmmm. Yes I am. I wonder how I missed that. Thanks! As bdi_set_min_ratio doesn't touch bdi->dev, there seems to be no need for the test, or the warning. I wonder if it would make sense to move the bdi_set_min_ratio() call to bdi_destroy, and discard bdi_unregister?? There is a comment which suggests bdi_unregister might be of use later, but it might be best to have a clean slate in which to add whatever might be needed?? NeilBrown diff --git a/block/genhd.c b/block/genhd.c index e351fc521053..1d4435478e8a 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -657,7 +657,6 @@ void del_gendisk(struct gendisk *disk) disk->flags &=3D ~GENHD_FL_UP; =20 sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi"); - bdi_unregister(&disk->queue->backing_dev_info); blk_unregister_queue(disk); blk_unregister_region(disk_devt(disk), disk->minors); =20 diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index aff923ae8c4b..d87d8eced064 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -116,7 +116,6 @@ __printf(3, 4) int bdi_register(struct backing_dev_info *bdi, struct device *parent, const char *fmt, ...); int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev); -void bdi_unregister(struct backing_dev_info *bdi); int __must_check bdi_setup_and_register(struct backing_dev_info *, char *); void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages, enum wb_reason reason); diff --git a/include/trace/events/writeback.h b/include/trace/events/writeb= ack.h index 880dd7437172..c178d13d6f4c 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -250,7 +250,6 @@ DEFINE_EVENT(writeback_class, name, \ DEFINE_WRITEBACK_EVENT(writeback_nowork); DEFINE_WRITEBACK_EVENT(writeback_wake_background); DEFINE_WRITEBACK_EVENT(writeback_bdi_register); -DEFINE_WRITEBACK_EVENT(writeback_bdi_unregister); =20 DECLARE_EVENT_CLASS(wbc_class, TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi), diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 6dc4580df2af..000e7b3b9896 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -359,23 +359,6 @@ static void bdi_wb_shutdown(struct backing_dev_info *b= di) flush_delayed_work(&bdi->wb.dwork); } =20 -/* - * Called when the device behind @bdi has been removed or ejected. - * - * We can't really do much here except for reducing the dirty ratio at - * the moment. In the future we should be able to set a flag so that - * the filesystem can handle errors at mark_inode_dirty time instead - * of only at writeback time. - */ -void bdi_unregister(struct backing_dev_info *bdi) -{ - if (WARN_ON_ONCE(!bdi->dev)) - return; - - bdi_set_min_ratio(bdi, 0); -} -EXPORT_SYMBOL(bdi_unregister); - static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info = *bdi) { memset(wb, 0, sizeof(*wb)); @@ -443,6 +426,7 @@ void bdi_destroy(struct backing_dev_info *bdi) int i; =20 bdi_wb_shutdown(bdi); + bdi_set_min_ratio(bdi, 0); =20 WARN_ON(!list_empty(&bdi->work_list)); WARN_ON(delayed_work_pending(&bdi->wb.dwork)); --Sig_/a/y=o1PKzbldPLSytCnnabX Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIVAwUBVT/6yznsnt1WYoG5AQJz9Q/9GlKTZ1e3UXcDuQ8Sh2wC9nYbDSvE4pKP 0UEMZs8A/Vs9SGPsztRwBlc3voXEZZPxul4Tkp4NVAz0saHER6PVw+Lit+i3am2x jEgQDh/NX2agzxxAps9lihsGpIM3ueO3C1updmR4VR9eAVZ6eVgXXa26M6HL6zoG nXmOasCw6hN4pWZZYZduw9gRXNXwgI6+JKZAo7mJbv3sxooMrAS+JlCDYOoP36GW NYy61w4dCmPPVXMQW4IbUgCVwfL/30mUJiBHlx5iRIfG8gn2v/kqLUZsBTIw/t7w H569vT5Tl5Z3Z03nsxbJo+cMSBJV42Zc9j2yB5WTir6OPRTW3gz2B1yBaUUPWWb2 oLfrxlf2Ci2JBkL0MJVgQK/WCTBY2MB2OSy78oPy/3fBgQIDODw/n/AryFgGpuOc uFNY6/3jcMSD8Zx/0pwSuCveSkzHBZuuy9qD8R7L0xa1yQwwsreZZfzonWtjHCo0 017a41a+CX3KNhccx3IaezS5wOHF4b7Deqtg/Dt7CUSkPchuH4K144t+V3Dzg2Ny dT+nGYmtTYnnZt90IezEuhxyHSf1Vz6ArBiLrCnzAa8wVevLUPyaTkaaFwBbr8y2 EECADzrqpK0PxgL2bz2/fcsrVFHcqsZH2TBEsFSscgNrQtI1/h1CbRM/pYdL/ZnY YxDdQOdRrvs= =6SHG -----END PGP SIGNATURE----- --Sig_/a/y=o1PKzbldPLSytCnnabX--