[LU-4858] Race when reading ofd proc entries while unmounting OST

• Type: Bug
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.6.0, Lustre 2.5.2
• Affects Version/s: Lustre 2.6.0, Lustre 2.5.1, Lustre 2.4.3
• Labels: mn4
• Environment: Affects any OSS with any environment.
• Severity: 3
• Assignee: Lai Siyao
• Reporter: James A Simmons

Description

This bug was discovered due to the fact we run a utility that monitors the OST stats from /proc/fs/lustre/obdfilter/fsname-OSTXXXX. These stats were still being accessed while the test file system was taken down.

<4>[85795.199509] Lustre: server umount a1_thin-OST0129 complete
<0>[85795.339106] LustreError: 9005:0:(dt_object.h:1257:dt_statfs()) ASSERTION( dev ) failed:
<0>[85795.357847] LustreError: 9005:0:(dt_object.h:1257:dt_statfs()) LBUG
<4>[85795.377690] Pid: 9005, comm: cerebrod
<4>[85795.387927]
<4>[85795.387928] Call Trace:
<4>[85795.406853] [<ffffffffa03d4895>] libcfs_debug_dumpstack+0x55/0x80 [libcfs]
<4>[85795.427104] [<ffffffffa03d4e97>] lbug_with_loc+0x47/0xb0 [libcfs]
<4>[85795.447295] [<ffffffffa0d8b3be>] ofd_statfs_internal+0x23e/0x2a0 [ofd]
<4>[85795.467649] [<ffffffffa0d8b487>] ofd_statfs+0x67/0x510 [ofd]
<4>[85795.487335] [<ffffffffa05496d0>] lprocfs_rd_filesfree+0x170/0x4c0 [obdclass]
<4>[85795.508376] [<ffffffff811e9823>] ? proc_reg_open+0xc3/0x160
<4>[85795.528056] [<ffffffff811e9760>] ? proc_reg_open+0x0/0x160
<4>[85795.547148] [<ffffffffa0546563>] lprocfs_fops_read+0xf3/0x1f0 [obdclass]
<4>[85795.567489] [<ffffffff811e9d9e>] proc_reg_read+0x7e/0xc0
<4>[85795.587040] [<ffffffff81181cb5>] vfs_read+0xb5/0x1a0
<4>[85795.597941] [<ffffffff81181df1>] sys_read+0x51/0x90
<4>[85795.617517] [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
<4>[85795.637694]
<0>[85795.647408] Kernel panic - not syncing: LBUG

We have core dumps as well.