On Mon, 16 Apr 2012 18:45:17 -0500 Jonathan Brassow <jbrassow@xxxxxxxxxx>
wrote:
> Neil,
>
> I have 3 bugs that I've been working on. Two I have fixed and one I
> have not, but have a question.
>
> The first patch (dm-raid-set-recovery-flags-on-resume) addresses the
> fact that some recovery flags are altered during suspend, but not
> corrected upon resume. I'm wondering if you think these flags would be
> better pushed into 'mddev_resume' rather that being altered in
> dm-raid.c?
I think setting MD_RECOVERY_NEEDED in mddev_resume makes perfect sense.
It is quite safe to set it at any time, and the one place where md.c calls
mddev_resume() it sets the flag immediately afterwards. So moving that
setting into mddev_resume() makes sense.
MD_RECOVERY_FROZEN I'm less sure about. If we clear it in mddev_resume(),
then as soon as you convert a RAID5 to a RAID6 it would start recovery of the
extra device, even if you had set sync_action to 'frozen' first. That would
be wrong.
I guess we are over-loading 'MD_RECOVERY_FROZEN' it bit. It means both
"user-space requested a freeze" and "resync temporarily disabled".
I wonder if md_stop_writes() only needs to set it temporarily, and to make
sure MD_RECOVERY_NEEDED isn't set when it completes. That might be enough??
However maybe it is easiest to just clear it in raid_resume() like you did.
>
> The second patch (dm-raid-record-and-handle-missing-devices) adds code
> to address the case where the user specifies particular array positions
> as missing. I don't have any significant questions about this patch.
I do :-)
md already does all the proper accounting for ->degraded, dm-raid shouldn't
need to.
Incrementing md.degraded in dev_parms shouldn't be needed as md_run is
subsequently called, and it sets md.degraded correctly.
incrementing it in read_disk_sb() and setting the Faulty flag is wrong. I
think it should just call md_error().
The other changes in that patch look OK.
>
> The 3rd issue I am seeing concerns how 'suspend' happens. Suspend
> should flush all outstanding I/O and quiesce. When I look at the code,
> I feel it should be doing this. ('md_stop_writes' is called and
> followed-up by a call to 'mddev_suspend', which quiesces the
> personality.) However, if I create a RAID1 device, suspend it, and then
> detach one of the legs, it does not show the changes written immediately
> before the suspend. If I issue a 'sync', then the changes do show-up.
> I confused as to why the suspend process doesn't seem to be pushing out
> the writes that have been issued. Any ideas?
That sounds like it is behaving exactly as I would expect.
You have written to the filesystem (and so to the pagecache) but the
filesystem hasn't written to the device yet. That happens after a time, or
on a 'sync' or 'fsync'.
You might be able to get the block device to ask the filesystem to flush
things out using freeze_bdev(), but I'm not sure of the details there.
It might not flush things, it might just ensure metadata is consistent - or
something.
NeilBrown
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