Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    bcache: only permit to recovery read error when cache device is clean

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d59b23795933678c9638fd20c942d2b4f3cd6185 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Mon, 30 Oct 2017 14:46:31 -0700
Subject: bcache: only permit to recovery read error when cache device is clean

From: Coly Li <colyli@suse.de>

commit d59b23795933678c9638fd20c942d2b4f3cd6185 upstream.

When bcache does read I/Os, for example in writeback or writethrough mode,
if a read request on cache device is failed, bcache will try to recovery
the request by reading from cached device. If the data on cached device is
not synced with cache device, then requester will get a stale data.

For critical storage system like database, providing stale data from
recovery may result an application level data corruption, which is
unacceptible.

With this patch, for a failed read request in writeback or writethrough
mode, recovery a recoverable read request only happens when cache device
is clean. That is to say, all data on cached device is up to update.

For other cache modes in bcache, read request will never hit
cached_dev_read_error(), they don't need this patch.

Please note, because cache mode can be switched arbitrarily in run time, a
writethrough mode might be switched from a writeback mode. Therefore
checking dc->has_data in writethrough mode still makes sense.

Changelog:
V4: Fix parens error pointed by Michael Lyle.
v3: By response from Kent Oversteet, he thinks recovering stale data is a
    bug to fix, and option to permit it is unnecessary. So this version
    the sysfs file is removed.
v2: rename sysfs entry from allow_stale_data_on_failure  to
    allow_stale_data_on_failure, and fix the confusing commit log.
v1: initial patch posted.

[small change to patch comment spelling by mlyle]

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reported-by: Arne Wolf <awolf@lenovo.com>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Nix <nix@esperi.org.uk>
Cc: Kai Krakow <hurikhan77@gmail.com>
Cc: Eric Wheeler <bcache@lists.ewheeler.net>
Cc: Junhui Tang <tang.junhui@zte.com.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/request.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -702,8 +702,16 @@ static void cached_dev_read_error(struct
 {
 	struct search *s = container_of(cl, struct search, cl);
 	struct bio *bio = &s->bio.bio;
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
 
-	if (s->recoverable) {
+	/*
+	 * If cache device is dirty (dc->has_dirty is non-zero), then
+	 * recovery a failed read request from cached device may get a
+	 * stale data back. So read failure recovery is only permitted
+	 * when cache device is clean.
+	 */
+	if (s->recoverable &&
+	    (dc && !atomic_read(&dc->has_dirty))) {
 		/* Retry from the backing device: */
 		trace_bcache_read_retry(s->orig_bio);
 


Patches currently in stable-queue which might be from colyli@suse.de are

queue-4.9/bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
queue-4.9/bcache-check-ca-alloc_thread-initialized-before-wake-up-it.patch

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Eddie Chapman]

On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>      bcache: only permit to recovery read error when cache device is clean
> 
> to the 4.9-stable tree which can be found at:
>      http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>       bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
> and it can be found in the queue-4.9 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

Hi Greg,

This patch is an important fix for a possible data corruption issue, but 
it also introduces a bug that can produce read errors under certain 
circumstances. The issue introduced by this patch is not as severe as 
the issue it fixes, but can lead to e.g. upper layer fs remounting read 
only. In my environment upper layer handled it badly and indirectly 
resulted in data loss (not directly bcache's fault of course).

Michael Lyle CC'd the stable list with a follow up fix for the issue 
introduced by this patch, on 24th Nov, subject "bcache: recover data 
from backing when data is clean".

However, the followup fix is not in Linus' tree yet, only in Michael's. 
I guess that means you can't pick it up yet. Never-the-less I felt it 
important to point this out here.

thanks,
Eddie

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Jens Axboe]

On 11/27/2017 09:45 AM, Eddie Chapman wrote:
> On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
>>
>> This is a note to let you know that I've just added the patch titled
>>
>>      bcache: only permit to recovery read error when cache device is clean
>>
>> to the 4.9-stable tree which can be found at:
>>      http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>>
>> The filename of the patch is:
>>       bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
>> and it can be found in the queue-4.9 subdirectory.
>>
>> If you, or anyone else, feels it should not be added to the stable tree,
>> please let <stable@vger.kernel.org> know about it.
> 
> Hi Greg,
> 
> This patch is an important fix for a possible data corruption issue, but 
> it also introduces a bug that can produce read errors under certain 
> circumstances. The issue introduced by this patch is not as severe as 
> the issue it fixes, but can lead to e.g. upper layer fs remounting read 
> only. In my environment upper layer handled it badly and indirectly 
> resulted in data loss (not directly bcache's fault of course).
> 
> Michael Lyle CC'd the stable list with a follow up fix for the issue 
> introduced by this patch, on 24th Nov, subject "bcache: recover data 
> from backing when data is clean".
> 
> However, the followup fix is not in Linus' tree yet, only in Michael's. 
> I guess that means you can't pick it up yet. Never-the-less I felt it 
> important to point this out here.

It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
go upstream shortly - but yes, probably should not add this one, before
both can be pulled in.

-- 
Jens Axboe

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Greg KH]

On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
> On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
> 
> > On 11/27/2017 09:45 AM, Eddie Chapman wrote:
> > > On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
> > >>
> > >> This is a note to let you know that I've just added the patch titled
> > >>
> > >>      bcache: only permit to recovery read error when cache device is
> > clean
> >
> 
> 
> > > Hi Greg,
> > >
> > > This patch is an important fix for a possible data corruption issue, but
> > > it also introduces a bug that can produce read errors under certain
> > > circumstances. The issue introduced by this patch is not as severe as
> > > the issue it fixes, but can lead to e.g. upper layer fs remounting read
> > > only. In my environment upper layer handled it badly and indirectly
> > > resulted in data loss (not directly bcache's fault of course).
> > >
> > > Michael Lyle CC'd the stable list with a follow up fix for the issue
> > > introduced by this patch, on 24th Nov, subject "bcache: recover data
> > > from backing when data is clean".
> > >
> > > However, the followup fix is not in Linus' tree yet, only in Michael's.
> > > I guess that means you can't pick it up yet. Never-the-less I felt it
> > > important to point this out here.
> >
> > It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
> > go upstream shortly - but yes, probably should not add this one, before
> > both can be pulled in.
> 
> 
> Thanks everyone for the quick reply on this.  I agree.

Ok, I've dropped this patch from all of the stable queues for now.

thanks,

greg k-h

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Greg KH]

On Tue, Nov 28, 2017 at 10:06:24AM +0100, Greg KH wrote:
> On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
> > On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
> > 
> > > On 11/27/2017 09:45 AM, Eddie Chapman wrote:
> > > > On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
> > > >>
> > > >> This is a note to let you know that I've just added the patch titled
> > > >>
> > > >>      bcache: only permit to recovery read error when cache device is
> > > clean
> > >
> > 
> > 
> > > > Hi Greg,
> > > >
> > > > This patch is an important fix for a possible data corruption issue, but
> > > > it also introduces a bug that can produce read errors under certain
> > > > circumstances. The issue introduced by this patch is not as severe as
> > > > the issue it fixes, but can lead to e.g. upper layer fs remounting read
> > > > only. In my environment upper layer handled it badly and indirectly
> > > > resulted in data loss (not directly bcache's fault of course).
> > > >
> > > > Michael Lyle CC'd the stable list with a follow up fix for the issue
> > > > introduced by this patch, on 24th Nov, subject "bcache: recover data
> > > > from backing when data is clean".
> > > >
> > > > However, the followup fix is not in Linus' tree yet, only in Michael's.
> > > > I guess that means you can't pick it up yet. Never-the-less I felt it
> > > > important to point this out here.
> > >
> > > It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
> > > go upstream shortly - but yes, probably should not add this one, before
> > > both can be pulled in.
> > 
> > 
> > Thanks everyone for the quick reply on this.  I agree.
> 
> Ok, I've dropped this patch from all of the stable queues for now.

Both now queued up, thanks.


greg k-h

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Eddie Chapman]

On 04/12/17 10:27, Greg KH wrote:
> On Tue, Nov 28, 2017 at 10:06:24AM +0100, Greg KH wrote:
>> On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
>>> On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>>> On 11/27/2017 09:45 AM, Eddie Chapman wrote:
>>>>> On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
>>>>>>
>>>>>> This is a note to let you know that I've just added the patch titled
>>>>>>
>>>>>>       bcache: only permit to recovery read error when cache device is
>>>> clean
>>>>
>>>
>>>
>>>>> Hi Greg,
>>>>>
>>>>> This patch is an important fix for a possible data corruption issue, but
>>>>> it also introduces a bug that can produce read errors under certain
>>>>> circumstances. The issue introduced by this patch is not as severe as
>>>>> the issue it fixes, but can lead to e.g. upper layer fs remounting read
>>>>> only. In my environment upper layer handled it badly and indirectly
>>>>> resulted in data loss (not directly bcache's fault of course).
>>>>>
>>>>> Michael Lyle CC'd the stable list with a follow up fix for the issue
>>>>> introduced by this patch, on 24th Nov, subject "bcache: recover data
>>>>> from backing when data is clean".
>>>>>
>>>>> However, the followup fix is not in Linus' tree yet, only in Michael's.
>>>>> I guess that means you can't pick it up yet. Never-the-less I felt it
>>>>> important to point this out here.
>>>>
>>>> It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
>>>> go upstream shortly - but yes, probably should not add this one, before
>>>> both can be pulled in.
>>>
>>>
>>> Thanks everyone for the quick reply on this.  I agree.
>>
>> Ok, I've dropped this patch from all of the stable queues for now.
> 
> Both now queued up, thanks.
> 
> 
> greg k-h
> 

Hi Greg,

I only see those two queued up for 4.14 and not any earlier kernels. You 
originally added the first patch to 3.18, 4.4 and 4.9. Are you still 
planning to add them both to those kernels?

thanks,
Eddie

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Greg KH]

On Mon, Dec 04, 2017 at 11:45:18PM +0000, Eddie Chapman wrote:
> On 04/12/17 10:27, Greg KH wrote:
> > On Tue, Nov 28, 2017 at 10:06:24AM +0100, Greg KH wrote:
> > > On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
> > > > On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
> > > > 
> > > > > On 11/27/2017 09:45 AM, Eddie Chapman wrote:
> > > > > > On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
> > > > > > > 
> > > > > > > This is a note to let you know that I've just added the patch titled
> > > > > > > 
> > > > > > >       bcache: only permit to recovery read error when cache device is
> > > > > clean
> > > > > 
> > > > 
> > > > 
> > > > > > Hi Greg,
> > > > > > 
> > > > > > This patch is an important fix for a possible data corruption issue, but
> > > > > > it also introduces a bug that can produce read errors under certain
> > > > > > circumstances. The issue introduced by this patch is not as severe as
> > > > > > the issue it fixes, but can lead to e.g. upper layer fs remounting read
> > > > > > only. In my environment upper layer handled it badly and indirectly
> > > > > > resulted in data loss (not directly bcache's fault of course).
> > > > > > 
> > > > > > Michael Lyle CC'd the stable list with a follow up fix for the issue
> > > > > > introduced by this patch, on 24th Nov, subject "bcache: recover data
> > > > > > from backing when data is clean".
> > > > > > 
> > > > > > However, the followup fix is not in Linus' tree yet, only in Michael's.
> > > > > > I guess that means you can't pick it up yet. Never-the-less I felt it
> > > > > > important to point this out here.
> > > > > 
> > > > > It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
> > > > > go upstream shortly - but yes, probably should not add this one, before
> > > > > both can be pulled in.
> > > > 
> > > > 
> > > > Thanks everyone for the quick reply on this.  I agree.
> > > 
> > > Ok, I've dropped this patch from all of the stable queues for now.
> > 
> > Both now queued up, thanks.
> > 
> > 
> > greg k-h
> > 
> 
> Hi Greg,
> 
> I only see those two queued up for 4.14 and not any earlier kernels. You
> originally added the first patch to 3.18, 4.4 and 4.9. Are you still
> planning to add them both to those kernels?

Ah, I forgot about that.  I'll go queue those up for the next round
after these kernels are released in a day or so.

thanks,

greg k-h

Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    bcache: only permit to recovery read error when cache device is clean

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d59b23795933678c9638fd20c942d2b4f3cd6185 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Mon, 30 Oct 2017 14:46:31 -0700
Subject: bcache: only permit to recovery read error when cache device is clean

From: Coly Li <colyli@suse.de>

commit d59b23795933678c9638fd20c942d2b4f3cd6185 upstream.

When bcache does read I/Os, for example in writeback or writethrough mode,
if a read request on cache device is failed, bcache will try to recovery
the request by reading from cached device. If the data on cached device is
not synced with cache device, then requester will get a stale data.

For critical storage system like database, providing stale data from
recovery may result an application level data corruption, which is
unacceptible.

With this patch, for a failed read request in writeback or writethrough
mode, recovery a recoverable read request only happens when cache device
is clean. That is to say, all data on cached device is up to update.

For other cache modes in bcache, read request will never hit
cached_dev_read_error(), they don't need this patch.

Please note, because cache mode can be switched arbitrarily in run time, a
writethrough mode might be switched from a writeback mode. Therefore
checking dc->has_data in writethrough mode still makes sense.

Changelog:
V4: Fix parens error pointed by Michael Lyle.
v3: By response from Kent Oversteet, he thinks recovering stale data is a
    bug to fix, and option to permit it is unnecessary. So this version
    the sysfs file is removed.
v2: rename sysfs entry from allow_stale_data_on_failure  to
    allow_stale_data_on_failure, and fix the confusing commit log.
v1: initial patch posted.

[small change to patch comment spelling by mlyle]

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reported-by: Arne Wolf <awolf@lenovo.com>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Nix <nix@esperi.org.uk>
Cc: Kai Krakow <hurikhan77@gmail.com>
Cc: Eric Wheeler <bcache@lists.ewheeler.net>
Cc: Junhui Tang <tang.junhui@zte.com.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/request.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -702,8 +702,16 @@ static void cached_dev_read_error(struct
 {
 	struct search *s = container_of(cl, struct search, cl);
 	struct bio *bio = &s->bio.bio;
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
 
-	if (s->recoverable) {
+	/*
+	 * If cache device is dirty (dc->has_dirty is non-zero), then
+	 * recovery a failed read request from cached device may get a
+	 * stale data back. So read failure recovery is only permitted
+	 * when cache device is clean.
+	 */
+	if (s->recoverable &&
+	    (dc && !atomic_read(&dc->has_dirty))) {
 		/* Retry from the backing device: */
 		trace_bcache_read_retry(s->orig_bio);
 


Patches currently in stable-queue which might be from colyli@suse.de are

queue-4.9/bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
queue-4.9/bcache-recover-data-from-backing-when-data-is-clean.patch

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Greg KH]

On Tue, Dec 05, 2017 at 08:49:56AM +0100, Greg KH wrote:
> On Mon, Dec 04, 2017 at 11:45:18PM +0000, Eddie Chapman wrote:
> > On 04/12/17 10:27, Greg KH wrote:
> > > On Tue, Nov 28, 2017 at 10:06:24AM +0100, Greg KH wrote:
> > > > On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
> > > > > On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
> > > > > 
> > > > > > On 11/27/2017 09:45 AM, Eddie Chapman wrote:
> > > > > > > On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
> > > > > > > > 
> > > > > > > > This is a note to let you know that I've just added the patch titled
> > > > > > > > 
> > > > > > > >       bcache: only permit to recovery read error when cache device is
> > > > > > clean
> > > > > > 
> > > > > 
> > > > > 
> > > > > > > Hi Greg,
> > > > > > > 
> > > > > > > This patch is an important fix for a possible data corruption issue, but
> > > > > > > it also introduces a bug that can produce read errors under certain
> > > > > > > circumstances. The issue introduced by this patch is not as severe as
> > > > > > > the issue it fixes, but can lead to e.g. upper layer fs remounting read
> > > > > > > only. In my environment upper layer handled it badly and indirectly
> > > > > > > resulted in data loss (not directly bcache's fault of course).
> > > > > > > 
> > > > > > > Michael Lyle CC'd the stable list with a follow up fix for the issue
> > > > > > > introduced by this patch, on 24th Nov, subject "bcache: recover data
> > > > > > > from backing when data is clean".
> > > > > > > 
> > > > > > > However, the followup fix is not in Linus' tree yet, only in Michael's.
> > > > > > > I guess that means you can't pick it up yet. Never-the-less I felt it
> > > > > > > important to point this out here.
> > > > > > 
> > > > > > It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
> > > > > > go upstream shortly - but yes, probably should not add this one, before
> > > > > > both can be pulled in.
> > > > > 
> > > > > 
> > > > > Thanks everyone for the quick reply on this.  I agree.
> > > > 
> > > > Ok, I've dropped this patch from all of the stable queues for now.
> > > 
> > > Both now queued up, thanks.
> > > 
> > > 
> > > greg k-h
> > > 
> > 
> > Hi Greg,
> > 
> > I only see those two queued up for 4.14 and not any earlier kernels. You
> > originally added the first patch to 3.18, 4.4 and 4.9. Are you still
> > planning to add them both to those kernels?
> 
> Ah, I forgot about that.  I'll go queue those up for the next round
> after these kernels are released in a day or so.

All now queued up.

greg k-h

Re: Patch "bcache: only permit to recovery read error when cache device is clean" has been added to the 4.9-stable tree

[Michael Lyle]

Cool, thank you very much.  -mpl

On Tue, Dec 5, 2017 at 6:30 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Tue, Dec 05, 2017 at 08:49:56AM +0100, Greg KH wrote:
>> On Mon, Dec 04, 2017 at 11:45:18PM +0000, Eddie Chapman wrote:
>> > On 04/12/17 10:27, Greg KH wrote:
>> > > On Tue, Nov 28, 2017 at 10:06:24AM +0100, Greg KH wrote:
>> > > > On Mon, Nov 27, 2017 at 09:35:02AM -0800, Michael Lyle wrote:
>> > > > > On Mon, Nov 27, 2017 at 9:01 AM, Jens Axboe <axboe@kernel.dk> wrote:
>> > > > >
>> > > > > > On 11/27/2017 09:45 AM, Eddie Chapman wrote:
>> > > > > > > On 27/11/17 16:06, gregkh@linuxfoundation.org wrote:
>> > > > > > > >
>> > > > > > > > This is a note to let you know that I've just added the patch titled
>> > > > > > > >
>> > > > > > > >       bcache: only permit to recovery read error when cache device is
>> > > > > > clean
>> > > > > >
>> > > > >
>> > > > >
>> > > > > > > Hi Greg,
>> > > > > > >
>> > > > > > > This patch is an important fix for a possible data corruption issue, but
>> > > > > > > it also introduces a bug that can produce read errors under certain
>> > > > > > > circumstances. The issue introduced by this patch is not as severe as
>> > > > > > > the issue it fixes, but can lead to e.g. upper layer fs remounting read
>> > > > > > > only. In my environment upper layer handled it badly and indirectly
>> > > > > > > resulted in data loss (not directly bcache's fault of course).
>> > > > > > >
>> > > > > > > Michael Lyle CC'd the stable list with a follow up fix for the issue
>> > > > > > > introduced by this patch, on 24th Nov, subject "bcache: recover data
>> > > > > > > from backing when data is clean".
>> > > > > > >
>> > > > > > > However, the followup fix is not in Linus' tree yet, only in Michael's.
>> > > > > > > I guess that means you can't pick it up yet. Never-the-less I felt it
>> > > > > > > important to point this out here.
>> > > > > >
>> > > > > > It's commit e393aa2446150536929140739f09c6ecbcbea7f0 in my tree and will
>> > > > > > go upstream shortly - but yes, probably should not add this one, before
>> > > > > > both can be pulled in.
>> > > > >
>> > > > >
>> > > > > Thanks everyone for the quick reply on this.  I agree.
>> > > >
>> > > > Ok, I've dropped this patch from all of the stable queues for now.
>> > >
>> > > Both now queued up, thanks.
>> > >
>> > >
>> > > greg k-h
>> > >
>> >
>> > Hi Greg,
>> >
>> > I only see those two queued up for 4.14 and not any earlier kernels. You
>> > originally added the first patch to 3.18, 4.4 and 4.9. Are you still
>> > planning to add them both to those kernels?
>>
>> Ah, I forgot about that.  I'll go queue those up for the next round
>> after these kernels are released in a day or so.
>
> All now queued up.
>
> greg k-h