[resend][bug] low-probability console lockups since 5.19

[Conor Dooley]

Hey all,

Been bisecting a bug that is causing a boot failure in my CI & have
ended up here.. The bug in question is a low(ish) probability lock up
of the serial console, I would estimate about 1-in-5 chance on the
boards I could actually trigger it on which it has taken me so long
to realise that this was an actual problem. Thinking back on it, there
were other failures that I would retroactively attribute to this
problem too, but I had earlycon disabled and I chalked the hangs at
"Starting kernel" down to pre-release hardware since the other boots
in a CI job would not fail (we boot the same config multiple times),
Silly me I guess!

In a boot failure (with earlycon & keep_bootcon enabled) I see the
likes of [0]:
[    0.485063] NFS: Registering the id_resolver key type
[    0.491051] Key type id_resolver registered
[    0.495743] Key type id_legacy registered
[    0.500528] nfs4filelayout_init: NFSv4 File Layout Driver Registering...
[    0.508010] nfs4flexfilelayout_init: NFSv4 Flexfile Layout Driver Registering...
[    0.516857] 9p: Installing v9fs 9p2000 file system support
[    0.524032] NET: Registered PF_ALG protocol family
[    0.529562] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 247)
[    0.537817] io scheduler mq-deadline registered
[    0.542889] io scheduler kyber registered
[    0.559682] microchip-pcie 2000000000.pcie: host bridge /soc/pcie@2000000000 ranges:
[    0.568431] microchip-pcie 2000000000.pcie:      MEM 0x2008000000..0x2087ffffff -> 0x0008000000
[    0.635633] microchip-pcie 2000000000.pcie: axi read request error
[    0.642602] microchip-pcie 2000000000.pcie: axi read timeout
[    0.776630] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.784133] microchip-pcie 2000000000.pcie: axi write request error
[    0.791100] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.798543] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.805981] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.813421] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.820859] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    0.828295] microchip-pcie 2000000000.pcie: sec error in axi2pcie buffer
[    1.579668] Freeing initrd memory: 7316K

The sec error stuff is unrelated & happens on good boots too - although
there are far fewer lines of "sec error" there [1] (excuse the message
duplication from the bootcon).

I was able to bisect the behaviour to this set of reverts, but I have
low confidence as to which commit specifically caused it - it's hard
to know that doing 20+ reboots on every commmit I built is enough to
make sure I did not make a mistake. I had initially started the
bisection between v6.0-rc6 & v6.0-rc1, and that lead me down a sub-tree
of net which is why the bisect log starts at a "random" commit as that
merge commit was the one blamed by the inital bisection.

git bisect start
# status: waiting for both good and bad commits
# bad: [5e8379351dbde61ea383e514f0f9ecb2c047cf4e] Merge tag 'net-5.19-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
git bisect bad 5e8379351dbde61ea383e514f0f9ecb2c047cf4e
# good: [4b0986a3613c92f4ec1bdc7f60ec66fea135991f] Linux 5.18
git bisect good 4b0986a3613c92f4ec1bdc7f60ec66fea135991f
# good: [fbe86daca0ba878b04fa241b85e26e54d17d4229] Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
git bisect good fbe86daca0ba878b04fa241b85e26e54d17d4229
# good: [2b8c612c6102f751e6e3e1bd425f64e9d3d3f638] kernel/reboot: Fix powering off using a non-syscall code paths
git bisect good 2b8c612c6102f751e6e3e1bd425f64e9d3d3f638
# good: [54c2cc79194c961a213c1d375fe3aa4165664cc4] Merge tag 'usb-5.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb
git bisect good 54c2cc79194c961a213c1d375fe3aa4165664cc4
# skip: [8f7ac50c97d30ae5ae48da3b516510d05a67b9e5] Merge tag 'sound-5.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect skip 8f7ac50c97d30ae5ae48da3b516510d05a67b9e5
# good: [cdd85786f4b3b9273e4376e69aa95a2d71722764] x86/tdx: Clarify RIP adjustments in #VE handler
git bisect good cdd85786f4b3b9273e4376e69aa95a2d71722764
# good: [8cc683833726912498130a0130fc3bd0d169ef59] Merge branch 'net-dp83822-fix-interrupt-floods'
git bisect good 8cc683833726912498130a0130fc3bd0d169ef59
# bad: [0840a7914caa14315a3191178a9f72c742477860] Merge tag 'char-misc-5.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
git bisect bad 0840a7914caa14315a3191178a9f72c742477860
# bad: [38bc4ac431684498126f9baa3a530e5a132f0173] Merge tag 'drm-fixes-2022-06-24' of git://anongit.freedesktop.org/drm/drm
git bisect bad 38bc4ac431684498126f9baa3a530e5a132f0173
# good: [399bd66e219e331976fe6fa6ab81a023c0c97870] Merge tag 'net-5.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
git bisect good 399bd66e219e331976fe6fa6ab81a023c0c97870
# bad: [a237cfd6b7469d6f5eeaa45f30128ab78b5281a5] Merge tag 'block-5.19-2022-06-24' of git://git.kernel.dk/linux-block
git bisect bad a237cfd6b7469d6f5eeaa45f30128ab78b5281a5
# good: [92f20ff72066d8d7e2ffb655c2236259ac9d1c5d] Merge tag 'pm-5.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
git bisect good 92f20ff72066d8d7e2ffb655c2236259ac9d1c5d
# bad: [598f2404879336277a4320ac5000394b873e049a] Merge tag 'io_uring-5.19-2022-06-24' of git://git.kernel.dk/linux-block
git bisect bad 598f2404879336277a4320ac5000394b873e049a
# good: [386e4fb6962b9f248a80f8870aea0870ca603e89] io_uring: use original request task for inflight tracking
git bisect good 386e4fb6962b9f248a80f8870aea0870ca603e89
# good: [2d9ef940f89e0ab4fde7ba6f769d82f2a450c35a] Revert "printk: extend console_lock for per-console locking"
git bisect good 2d9ef940f89e0ab4fde7ba6f769d82f2a450c35a
# bad: [07a22b61946f0b80065b0ddcc703b715f84355f5] Revert "printk: add functions to prefer direct printing"
git bisect bad 07a22b61946f0b80065b0ddcc703b715f84355f5
# bad: [5831788afb17b89c5b531fb60cbd798613ccbb63] Revert "printk: add kthread console printers"
git bisect bad 5831788afb17b89c5b531fb60cbd798613ccbb63
# first bad commit: [5831788afb17b89c5b531fb60cbd798613ccbb63] Revert "printk: add kthread console printers"

On 5831788afb17 ("Revert "printk: add kthread console printers"") or on
07a22b61946f ("Revert "printk: add functions to prefer direct printing"")
I was not able to reproduce the exact error conditions that I got on
the current HEAD or any of the commits along my bisection, but instead I
got something different [2]:

[    0.471992] 9p: Installing v9fs 9p2000 file system support
[    0.479049] NET: Registered PF_ALG protocol family
[    0.484585] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 247)
[    0.492813] io scheduler mq-deadline registered
[    0.497871] io scheduler kyber registered
[    0.513472] microchip-pcie 2000000000.pcie: host bridge /soc/pcie@2000000000 ranges:
[    0.522194] microchip-pcie 2000000000.pcie:      MEM 0x2008000000..0x2087ffffff -> 0x0008000000
[    0.588518] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer
[    0.596027] microchip-pcie 2000000000.pcie: ded error in pcie2axi buffer
[    0.603467] microchip-pcie 2000000000.pcie: axi read request error
[    0.610322] microchip-pcie 2000000000.pcie: axi read timeout
[    0.616603] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer
[    0.624025] microchip-pcie 2000000000.pcie: ded error in pcie2axi buffer
[    0.631450] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer
[    0.638877] microchip-pcie 2000000000.pcie: ded error in pcie2axi buffer
[    0.646300] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer
[    0.653725] microchip-pcie 2000000000.pcie: ded error in pcie2axi buffer
[    1.516378] Freeing initrd memory: 7336K
[    5.591881] mc_event_handler: 667402 callbacks suppressed
[    5.591909] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer
[    5.605290] microchip-pcie 2000000000.pcie: ded error in pcie2axi buffer
[    5.612704] microchip-pcie 2000000000.pcie: sec error in pcie2axi buffer

<truncated>

[   21.539878] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[   21.546651] rcu: 	0-...0: (1 GPs behind) idle=19f/1/0x4000000000000002 softirq=34/36 fqs=2626 
[   21.556177] 	(detected by 1, t=5256 jiffies, g=-1151, q=1143 ncpus=4)
[   21.563293] Task dump for CPU 0:
[   21.566860] task:swapper/0       state:R  running task     stack:    0 pid:    1 ppid:     0 flags:0x00000008
[   21.577823] Call Trace:

Unfortunately I do not really have any more information than that for
you, I am hoping that you (plural) could be of some help as to where
I should start looking - although after spending every evening this
week bisecting/setting up so that I could automate my bisection it'll
be a few days before I could really focus on this again.

My system is an embedded RISC-V dev board (PolarFire SoC Icicle kit).

There is also a failing build in the ClangBuiltLinux CI [3] that is
seeing similar symptoms, but I was unable to reproduce this problem
doing 1000s of reboots of a known-bad commit in QEMU myself.

LMK if you need any more info,
Conor.

[0] https://gist.githubusercontent.com/ConchuOD/575f4bfe3d68b9b32227740365b04401/raw/c69dfffd21183898edaeb223a9455ebc28edcf65/gistfile1.txt
[1] https://gist.github.com/ConchuOD/575f4bfe3d68b9b32227740365b04401?permalink_comment_id=4313185#gistcomment-4313185
[2] https://gist.github.com/ConchuOD/575f4bfe3d68b9b32227740365b04401?permalink_comment_id=4313202#gistcomment-4313202
[3] https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/3090070308/jobs/4999131449#step:5:270