[PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[Liu Bo]

The kernel oops happens at

kernel BUG at fs/btrfs/extent_io.c:2104!
...
RIP: clean_io_failure+0x263/0x2a0 [btrfs]

It's showing that read-repair code is using an improper mirror index.
This is due to the fact that compression read's endio hasn't recorded
the failed mirror index in %cb->orig_bio.

With this, btrfs's read-repair can work properly on reading compressed
data.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reported-by: Paul Jones <paul@pauljones.id.au>
---
 fs/btrfs/compression.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d2ef9ac..9a4ccdf 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -107,6 +107,7 @@ static void end_compressed_bio_read(struct bio *bio)
 	struct inode *inode;
 	struct page *page;
 	unsigned long index;
+	unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
 	int ret;
 
 	if (bio->bi_status)
@@ -118,6 +119,14 @@ static void end_compressed_bio_read(struct bio *bio)
 	if (!refcount_dec_and_test(&cb->pending_bios))
 		goto out;
 
+	/*
+	 * Record the correct mirror_num in cb->orig_bio so that
+	 * read-repair can work properly.
+	 */
+	ASSERT(btrfs_io_bio(cb->orig_bio));
+	btrfs_io_bio(cb->orig_bio)->mirror_num = mirror;
+	cb->mirror_num = mirror;
+
 	inode = cb->inode;
 	ret = check_compressed_csum(BTRFS_I(inode), cb,
 				    (u64)bio->bi_iter.bi_sector << 9);
-- 
2.9.4

[PATCH 2/2] Btrfs: skip checksum when reading compressed data if some IO have failed

[Liu Bo]

Currently even if the underlying disk reports failure on IO,
compressed read endio still gets to verify checksum and reports it as
a checksum error.

In fact, if some IO have failed during reading a compressed data
extent , there's no way the checksum could match, therefore, we can
skip that in order to return error quickly to the upper layer.

Please note that we need to do this after recording the failed mirror
index so that read-repair in the upper layer's endio can work
properly.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/compression.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 9a4ccdf..d8d4678 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -108,7 +108,7 @@ static void end_compressed_bio_read(struct bio *bio)
 	struct page *page;
 	unsigned long index;
 	unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
-	int ret;
+	int ret = 0;
 
 	if (bio->bi_status)
 		cb->errors = 1;
@@ -127,6 +127,13 @@ static void end_compressed_bio_read(struct bio *bio)
 	btrfs_io_bio(cb->orig_bio)->mirror_num = mirror;
 	cb->mirror_num = mirror;
 
+	/*
+	 * Some IO in this cb have failed, just skip checksum as there
+	 * is no way it could be correct.
+	 */
+	if (cb->errors == 1)
+		goto csum_failed;
+
 	inode = cb->inode;
 	ret = check_compressed_csum(BTRFS_I(inode), cb,
 				    (u64)bio->bi_iter.bi_sector << 9);
-- 
2.9.4

Re: [PATCH 2/2] Btrfs: skip checksum when reading compressed data if some IO have failed

[David Sterba]

On Wed, Sep 20, 2017 at 05:50:19PM -0600, Liu Bo wrote:
> Currently even if the underlying disk reports failure on IO,
> compressed read endio still gets to verify checksum and reports it as
> a checksum error.
> 
> In fact, if some IO have failed during reading a compressed data
> extent , there's no way the checksum could match, therefore, we can
> skip that in order to return error quickly to the upper layer.
> 
> Please note that we need to do this after recording the failed mirror
> index so that read-repair in the upper layer's endio can work
> properly.
> 
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

Reviewed-by: David Sterba <dsterba@suse.com>

Re: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[David Sterba]

On Wed, Sep 20, 2017 at 05:50:18PM -0600, Liu Bo wrote:
> The kernel oops happens at
> 
> kernel BUG at fs/btrfs/extent_io.c:2104!
> ...
> RIP: clean_io_failure+0x263/0x2a0 [btrfs]
> 
> It's showing that read-repair code is using an improper mirror index.
> This is due to the fact that compression read's endio hasn't recorded
> the failed mirror index in %cb->orig_bio.

This sounds like the corner case of raid1 repair that was reported i the
past and actually is the only thing because of which we are not so
comfortable to mark raid1 'completely ok' in the Status page.

Re: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[David Sterba]

On Wed, Sep 20, 2017 at 05:50:18PM -0600, Liu Bo wrote:
> The kernel oops happens at
> 
> kernel BUG at fs/btrfs/extent_io.c:2104!
> ...
> RIP: clean_io_failure+0x263/0x2a0 [btrfs]
> 
> It's showing that read-repair code is using an improper mirror index.
> This is due to the fact that compression read's endio hasn't recorded
> the failed mirror index in %cb->orig_bio.
> 
> With this, btrfs's read-repair can work properly on reading compressed
> data.
> 
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> Reported-by: Paul Jones <paul@pauljones.id.au>

Reviewed-by: David Sterba <dsterba@suse.com>

RE: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[Paul Jones]

> -----Original Message-----
> From: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-
> owner@vger.kernel.org] On Behalf Of David Sterba
> Sent: Sunday, 24 September 2017 11:46 PM
> To: Liu Bo <bo.li.liu@oracle.com>
> Cc: linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed
> data
> 
> On Wed, Sep 20, 2017 at 05:50:18PM -0600, Liu Bo wrote:
> > The kernel oops happens at
> >
> > kernel BUG at fs/btrfs/extent_io.c:2104!
> > ...
> > RIP: clean_io_failure+0x263/0x2a0 [btrfs]
> >
> > It's showing that read-repair code is using an improper mirror index.
> > This is due to the fact that compression read's endio hasn't recorded
> > the failed mirror index in %cb->orig_bio.
> >
> > With this, btrfs's read-repair can work properly on reading compressed
> > data.
> >
> > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > Reported-by: Paul Jones <paul@pauljones.id.au>
> 
> Reviewed-by: David Sterba <dsterba@suse.com>

Tested-by: <paul@pauljones.id.au>
For both patches.

I caused the same thing to happen again, this time by unplugging the wrong hard drive. Applied the patches and problem (BUG_ON) is gone.
Should this also go to stable? Seems like a rather glaring problem to me.

Paul.

Re: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

[David Sterba]

On Tue, Sep 26, 2017 at 08:41:27AM +0000, Paul Jones wrote:
> > -----Original Message-----
> > From: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-
> > owner@vger.kernel.org] On Behalf Of David Sterba
> > Sent: Sunday, 24 September 2017 11:46 PM
> > To: Liu Bo <bo.li.liu@oracle.com>
> > Cc: linux-btrfs@vger.kernel.org
> > Subject: Re: [PATCH 1/2] Btrfs: fix kernel oops while reading compressed
> > data
> > 
> > On Wed, Sep 20, 2017 at 05:50:18PM -0600, Liu Bo wrote:
> > > The kernel oops happens at
> > >
> > > kernel BUG at fs/btrfs/extent_io.c:2104!
> > > ...
> > > RIP: clean_io_failure+0x263/0x2a0 [btrfs]
> > >
> > > It's showing that read-repair code is using an improper mirror index.
> > > This is due to the fact that compression read's endio hasn't recorded
> > > the failed mirror index in %cb->orig_bio.
> > >
> > > With this, btrfs's read-repair can work properly on reading compressed
> > > data.
> > >
> > > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > > Reported-by: Paul Jones <paul@pauljones.id.au>
> > 
> > Reviewed-by: David Sterba <dsterba@suse.com>
> 
> Tested-by: <paul@pauljones.id.au>
> For both patches.

Thanks for testing.

> I caused the same thing to happen again, this time by unplugging the
> wrong hard drive. Applied the patches and problem (BUG_ON) is gone.
> Should this also go to stable? Seems like a rather glaring problem to me.

Yes it should and will be forwarded there once it's merged to Linus'
tree.