Re: [Regression, Bisected] dm-crypt IO failures with active slub_debug in 4.12 and later

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Nov 02 2017 at  4:39pm -0400,
Bruno Prémont <bonbons@sysophe.eu> wrote:

> Hi,
> 
> Between 4.11 and 4.12 I stopped being able to boot my system with root
> partition encrypted with dm-crypt (issue still present in 4.14-rc7).
> The system was able to open the dm-crypt device and read-only mount the
> XFS root partition on it.
> Later read-write remounting though caused XFS to shutdown the filesystem
> on IO error.
> 
> Some reports found online indicated a possible coincidence with stack
> protection or the like as well as use of slub_debug, the latter causing
> the IO errors to surface for me (I have slub_debug=ZP on my kernel
> cmdline).
> 
> I finally got time to go and bisect in order to find the triggering
> patch. Bisect log:
> 
> # good: [a351e9b9fc24e982ec2f0e76379a49826036da12] Linux 4.11
> git bisect good a351e9b9fc24e982ec2f0e76379a49826036da12
> # bad: [6f7da290413ba713f0cdd9ff1a2a9bb129ef4f6c] Linux 4.12
> git bisect bad 6f7da290413ba713f0cdd9ff1a2a9bb129ef4f6c
> # bad: [2bd80401743568ced7d303b008ae5298ce77e695] Merge tag 'gpio-v4.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio
> git bisect bad 2bd80401743568ced7d303b008ae5298ce77e695
> # good: [8d65b08debc7e62b2c6032d7fe7389d895b92cbc] Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
> git bisect good 8d65b08debc7e62b2c6032d7fe7389d895b92cbc
> # good: [8b03d1ed2c43a2ba5ef3381322ee4515b97381bf] Merge branch 'linux-4.12' of git://github.com/skeggsb/linux into drm-next
> git bisect good 8b03d1ed2c43a2ba5ef3381322ee4515b97381bf
> # bad: [e897f267c51812bfecec45771a2d835c1a2bdacf] Merge tag 'backlight-next-4.12' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight
> git bisect bad e897f267c51812bfecec45771a2d835c1a2bdacf
> # good: [46f0537b1ecf672052007c97f102a7e6bf0791e4] Merge branch 'stable-4.12' of git://git.infradead.org/users/pcmoore/audit
> git bisect good 46f0537b1ecf672052007c97f102a7e6bf0791e4
> # good: [20d5c84bef067b7e804a163e2abca16c47125bad] Merge remote-tracking branches 'asoc/topic/wm8960', 'asoc/topic/wm8978' and 'asoc/topic/zte-tdm' into asoc-next
> git bisect good 20d5c84bef067b7e804a163e2abca16c47125bad
> # bad: [7b66f13207e60e7c550af730986e77e38a0c69a3] Merge tag 'for-4.12/dm-post-merge-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
> git bisect bad 7b66f13207e60e7c550af730986e77e38a0c69a3
> # good: [dd7a8f5dee81ffb1794df1103f07c63fd4f1d766] md/raid5: make chunk_aligned_read() split bios more cleanly.
> git bisect good dd7a8f5dee81ffb1794df1103f07c63fd4f1d766
> # bad: [6625d903253eb6f003849823e22d7b8de5bfb5b2] dm integrity: use hex2bin instead of open-coded variant
> git bisect bad 6625d903253eb6f003849823e22d7b8de5bfb5b2
> # bad: [449b668ce0b9069fcaafa6344c7f10fa2ba9632e] dm cache: set/clear the cache core's dirty_bitset when loading mappings
> git bisect bad 449b668ce0b9069fcaafa6344c7f10fa2ba9632e
> # good: [33d2f09fcb357fd1861c4959d1d3505492bf91f8] dm crypt: introduce new format of cipher with "capi:" prefix
> git bisect good 33d2f09fcb357fd1861c4959d1d3505492bf91f8
> # bad: [ff3af92b4461be773337111daea80bb91b2cd545] dm crypt: use shifts instead of sector_div
> git bisect bad ff3af92b4461be773337111daea80bb91b2cd545
> # bad: [1aa0efd4210df1c57764b77040a6615bc9b3ac0f] dm integrity: factor out create_journal() from dm_integrity_ctr()
> git bisect bad 1aa0efd4210df1c57764b77040a6615bc9b3ac0f
> # bad: [8f0009a225171cc1b76a6b443de5137b26e1374b] dm crypt: optionally support larger encryption sector size
> git bisect bad 8f0009a225171cc1b76a6b443de5137b26e1374b
> # first bad commit: [8f0009a225171cc1b76a6b443de5137b26e1374b] dm crypt: optionally support larger encryption sector size
> 
> In order to test on 4.12 I had to revert the following commits,
> the first two having been applied on top of bad commit:
>   583fe7474c05ee5523e14ef791ea59604cd846dc (dm crypt: fix large block integrity support)
>   ff3af92b4461be773337111daea80bb91b2cd545 (dm crypt: use shifts instead of sector_div)
>   8f0009a225171cc1b76a6b443de5137b26e1374b (dm crypt: optionally support larger encryption sector size)
> 
> From looking at 8f0009a225171cc1b76a6b443de5137b26e1374b I can't spot
> direct cause though I assume there might be a mismatch in memory
> allocation versus access sizes as a consequence of support for larger
> encryption sector size (someplace 512 byte versus page size access
> tripping on memory poison?).

Thanks for bisecting this.

Can you apply the following debug patch to see if either of these newer
-EIO returns (introduced by commit 8f0009a225) are causing you problems
for some reason?

Thanks

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 05acc42..daefe37 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1056,7 +1056,7 @@ static int crypt_convert_block_aead(struct crypt_config *cc,
 	BUG_ON(cc->integrity_iv_size && cc->integrity_iv_size != cc->iv_size);
 
 	/* Reject unexpected unaligned bio. */
-	if (unlikely(bv_in.bv_offset & (cc->sector_size - 1)))
+	if (WARN_ON_ONCE(unlikely(bv_in.bv_offset & (cc->sector_size - 1)))))
 		return -EIO;
 
 	dmreq = dmreq_of_req(cc, req);
@@ -1149,7 +1149,7 @@ static int crypt_convert_block_skcipher(struct crypt_config *cc,
 	int r = 0;
 
 	/* Reject unexpected unaligned bio. */
-	if (unlikely(bv_in.bv_offset & (cc->sector_size - 1)))
+	if (WARN_ON_ONCE(unlikely(bv_in.bv_offset & (cc->sector_size - 1))))
 		return -EIO;
 
 	dmreq = dmreq_of_req(cc, req);