On Tue, 2018-12-18 at 16:45 +0100, Greg KH wrote:
> On Tue, Dec 18, 2018 at 04:34:46PM +0100, Greg KH wrote:
> > On Tue, Dec 18, 2018 at 10:19:39AM -0500, Sasha Levin wrote:
> > > On Tue, Dec 18, 2018 at 04:02:21PM +0100,
> > > gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> > > > The patch below does not apply to the 4.19-stable tree.
> > > > If someone wants it applied there, or to any other stable or
> > > > longterm
> > > > tree, then please email the backport, including the original git
> > > > commit
> > > > id to <stable@xxxxxxxxxxxxxxx>.
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > > >
> > > > ------------------ original commit in Linus's tree -----------
> > > > -------
> > > >
> > > > > From d57f9da890696af1484f4a47f7f123560197865a Mon Sep 17
> > > > > 00:00:00 2001
> > > > From: Damien Le Moal <damien.lemoal@xxxxxxx>
> > > > Date: Fri, 30 Nov 2018 15:31:48 +0900
> > > > Subject: [PATCH] dm zoned: Fix target BIO completion handling
> > > >
> > > > struct bioctx includes the ref refcount_t to track the number of
> > > > I/O
> > > > fragments used to process a target BIO as well as ensure that
> > > > the zone
> > > > of the BIO is kept in the active state throughout the lifetime
> > > > of the
> > > > BIO. However, since decrementing of this reference count is done
> > > > in the
> > > > target .end_io method, the function bio_endio() must be called
> > > > multiple
> > > > times for read and write target BIOs, which causes problems with
> > > > the
> > > > value of the __bi_remaining struct bio field for chained BIOs
> > > > (e.g. the
> > > > clone BIO passed by dm core is large and splits into fragments
> > > > by the
> > > > block layer), resulting in incorrect values and inconsistencies
> > > > with the
> > > > BIO_CHAIN flag setting. This is turn triggers the BUG_ON() call:
> > > >
> > > > BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);
> > > >
> > > > in bio_remaining_done() called from bio_endio().
> > > >
> > > > Fix this ensuring that bio_endio() is called only once for any
> > > > target
> > > > BIO by always using internal clone BIOs for processing any read
> > > > or
> > > > write target BIO. This allows reference counting using the
> > > > target BIO
> > > > context counter to trigger the target BIO completion bio_endio()
> > > > call
> > > > once all data, metadata and other zone work triggered by the BIO
> > > > complete.
> > > >
> > > > Overall, this simplifies the code too as the target .end_io
> > > > becomes
> > > > unnecessary and differences between read and write BIO issuing
> > > > and
> > > > completion processing disappear.
> > > >
> > > > Fixes: 3b1a94c88b79 ("dm zoned: drive-managed zoned block device
> > > > target")
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
> > > > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> > >
> > > This patch depends on 092b5648760a ("dm zoned: target: use
> > > refcount_t
> > > for dm zoned reference counters"), it might make sense to just
> > > take it
> > > as is instead of backporting d57f9da89069.
> >
> > Ah, ok, let me see how tough the backport is...
>
> For 4.19, it was pretty easy. For 4.14.y, nah, it's too tough for me,
> I
> want someone who knows this code to do that work...
>
> thanks,
>
> greg k-h
Greg,
I just sent the backported patch to you and stable list. I re-tested as
well on top of 4.14.89 to make sure there were no mistakes.
Thank you.
Best regards.
--
Damien Le Moal
Western Digital Research
