Re: FAILED: patch "[PATCH] dm zoned: Fix target BIO completion handling" failed to apply to 4.19-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

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@linuxfoundation.org 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@vger.kernel.org>.
> > > 
> > > 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@wdc.com>
> > > 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@vger.kernel.org
> > > Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> > > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > 
> > 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