Hello Jens,
as Hannes and Christoph have reviewed and acked this set, is there
anything more I can do to get it merged?
Best regards,
Martin
On Wed, 2019-03-27 at 14:51 +0100, Martin Wilck wrote:
> The block layer currently can't distinguish between gendisk devices
> that
> don't support any media change events, and devices that do support
> them,
> but only for internal purposes. Therefore the check_events() function
> is
> called e.g. for ordinary non-removable SCSI disks. While these
> devices
> are not polled under normal conditions, the check_events function is
> called on certain synchronization points, in particular while the
> device
> is opened, closed, or probed.
>
> Under unfavorable conditions this can lead to processes being stalled
> on
> a blocked queue: a close() schedules a work item for check_events()
> which gets blocked in the work queue, and subsequent open() tries to
> flush the workqueue. The flush then stalls too, as long as the the
> blocked work item can't finish.
>
> In principle, the gendisk->events field would make it very easy for
> the
> block layer to check only for events actually supported by the
> device.
> Currently this is impossible, because there are lots of drivers which
> don't set gendisk->events although they implement the check_events()
> method. This was introduced in commit 7c88a168da80 ("block: don't
> propagate unlisted DISK_EVENTs to userland") and follow-up patches
> because uevent generation by these drivers was found to possibly
> generate infinite event loops between kernel and user space. A side
> effect of these patches was that the distinction between such devices
> and devices supporting no events at all was lost.
>
> This series implements a slightly different approach to event
> handling
> and uevent suppression. The drivers are changed to set the events
> field
> again. Whether or not uevents should be generated is controlled by a
> separate flag bit, which is only set by the drivers that are known to
> generate proper uevents (sd and sr). Once this is done, devices that
> don't support any media change events can be clearly identified, and
> the
> whole events checking code path can be skipped. This simplifies
> handling
> of non-removable SCSI disks.
>
> I have tested this with removable and non-removable SCSI disks, SCSI
> cdrom, and ide-cd.
>
> This patch set targets the same problem as Hannes' late submission
> "sd:
> skip non-removable devices in sd_check_events()".
>
> Changes in v3:
>
> - Improved formatting of commit messages (Christoph)
> - 2/5: Rather than adding the event flag bits to the "events" field,
> add a new field "event_flags" to struct gendisk (Christoph)
> - 2/5: Add a pair of parentheses around flag test (Christoph)
>
> Changes in v2:
>
> Removed the unused async_events field from struct gendisk.
> This simplifies the event handling logic a bit.
>
> Martin Wilck (5):
> block: genhd: remove async_events field
> block: disk_events: introduce event flags
> Revert "ide: unexport DISK_EVENT_MEDIA_CHANGE for ide-gd and ide-
> cd"
> Revert "block: unexport DISK_EVENT_MEDIA_CHANGE for legacy/fringe
> drivers"
> block: check_events: don't bother with events if unsupported
>
> block/genhd.c | 48 ++++++++++++++++++++++------------
> ----
> drivers/block/amiflop.c | 1 +
> drivers/block/ataflop.c | 1 +
> drivers/block/floppy.c | 1 +
> drivers/block/paride/pcd.c | 1 +
> drivers/block/paride/pd.c | 1 +
> drivers/block/paride/pf.c | 1 +
> drivers/block/pktcdvd.c | 1 -
> drivers/block/swim.c | 1 +
> drivers/block/swim3.c | 1 +
> drivers/block/xsysace.c | 1 +
> drivers/cdrom/gdrom.c | 1 +
> drivers/ide/ide-cd.c | 1 +
> drivers/ide/ide-cd_ioctl.c | 5 ++--
> drivers/ide/ide-gd.c | 6 +++--
> drivers/scsi/sd.c | 1 +
> drivers/scsi/sr.c | 1 +
> include/linux/genhd.h | 11 +++++++--
> 18 files changed, 57 insertions(+), 27 deletions(-)
>
--
Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
