** Changed in: linux-azure-cvm (Ubuntu Focal)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1971164
Title:
[Azure][CVM] hv/bounce buffer: Fix a race that can fail disk detection
Status in linux-azure-cvm package in Ubuntu:
Invalid
Status in linux-azure-cvm source package in Focal:
Fix Committed
Bug description:
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
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