[Azure][CVM] hv/bounce buffer: Fix a race that can fail disk detection

[Tim Gardner]

SRU Justification

[Impact]

The linux-azure-cvm kernel (e.g. Ubuntu-azure-cvm-5.4.0-1078.81+cvm1) has a race condition bug in the Linux vmbus bounce buffer code (drivers/hv/hv_bounce.c), and as a result somtimes the kenrel fails to detect some of the SCSI disks, and the Linux dmesg log may show one of the 2 messages:

#1: [ 2.995732] sd 3:0:0:3: [sdd] Sector size 0 reported, assuming 512.

#2: [ 3.651293] scsi host3: scsi scan: INQUIRY result too short (5), using 36

Sometimes I see a strange call-trace (the 'order's is 18, if I print it)
2022-04-26T20:10:18,398144+00:00 kmalloc_order_trace+0x1e/0x80
2022-04-26T20:10:18,398147+00:00 __kmalloc+0x3ae/0x4c0
2022-04-26T20:10:18,398150+00:00 __scsi_scan_target+0x283/0x590
2022-04-26T20:10:18,398155+00:00 scsi_scan_channel.part.16+0x62/0x80
2022-04-26T20:10:18,398158+00:00 scsi_scan_host_selected+0xd5/0x150
2022-04-26T20:10:18,398160+00:00 store_scan+0xc8/0xe0
(This is very strange because 'order 18' means (1 << 18) * 4096 bytes = 1GBytes.)

After some investigation, we eventually got the root cause and made a fix:
https://github.com/dcui/linux-azure-cvm/commit/ddde4dc33242794000e1d9667a5f9cfa31c15fdf

With the fix, we no longer see the above strange symptoms.
Please include the fix into the next release of the v5.4 linux-azure-cvm kernel. Thanks!

[Test case]

Microsoft tested

[Where things could go wrong]

Some SCSI drives may continue to go undetected.

[Other Info]

SF: #00335631

[Tim Gardner (timg-tpi)]

Patch submitted: https://lists.ubuntu.com/archives/kernel-team/2022-May/129853.html

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux-azure-cvm/5.4.0-1080.83+cvm1 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-focal' to 'verification-done-focal'. If the problem still exists, change the tag 'verification-needed-focal' to 'verification-failed-focal'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Tim Gardner (timg-tpi)]

MSFT tested. Marking verification-done-focal

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-azure-cvm - 5.4.0-1080.83+cvm1

---------------
linux-azure-cvm (5.4.0-1080.83+cvm1) focal; urgency=medium

  * focal/linux-azure-cvm: 5.4.0-1080.83+cvm1 -proposed tracker (LP: #1973948)

  * [Azure][CVM] hv/bounce buffer: Fix a race that can fail disk detection
    (LP: #1971164)
    - SAUCE: hv/bounce buffer: Fix a race that can fail disk detection

  [ Ubuntu: 5.4.0-1080.83 ]

  * focal/linux-azure: 5.4.0-1080.83 -proposed tracker (LP: #1973952)
  * focal/linux: 5.4.0-113.127 -proposed tracker (LP: #1973980)
  * CVE-2022-29581
    - net/sched: cls_u32: fix netns refcount changes in u32_change()
  * CVE-2022-1116
    - io_uring: fix fs->users overflow
  * ext4: limit length to bitmap_maxbytes (LP: #1972281)
    - ext4: limit length to bitmap_maxbytes - blocksize in punch_hole
  * Unprivileged users may use PTRACE_SEIZE to set PTRACE_O_SUSPEND_SECCOMP
    option (LP: #1972740)
    - ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE

 -- Marcelo Henrique Cerri <email address hidden> Mon, 23 May 2022 18:06:01 -0300