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Description of problem:

After update, io_setup failing due to exhausted aio contexts.

Nov 14 08:01:34 host lvm: io_setup failed
Nov 14 08:01:34 host lvm: Failed to create bcache io engine.
Nov 14 08:01:34 host lvm: No PV info found on /dev/xvdf for PVID .

[sosreport]$ cat proc/sys/fs/aio-max-nr 
65536
[sosreport]$ cat proc/sys/fs/aio-nr 
65536

Version-Release number of selected component (if applicable):

lvm2.x86_64 7:2.02.180-10.el7_6.2
device-mapper.x86_64 7:1.02.149-10.el7_6.2
kernel-3.10.0-957.el7

Steps to Reproduce:

In customer environment, all they have to do us update to levels
mentioned and run lvm command.

Actual results:

io_setup failure

Expected results:

io_setup success

Additional info:

Errors do not persist after downgrade lvm2.x86_64 7:2.02.177-4.el7 and
device-mapper.x86_64 7:1.02.146-4.el7.

Fixed by these two commits which fall back to using sync io when io_setup fails
(or if use_aio=0 in lvm.conf):

https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=f8ce9bf3bc38df8f89021517d7967d94ace129df

https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=cb5405ded86209979eef54433d0b90942b2f976a

A possible workaround is to increase the system's aio request limit by setting a larger fs.aio-max-nr using sysctl.

A bug fix release, 2.02.183, has been tagged upstream: https://sourceware.org/git/?p=lvm2.git;a=tag;h=f21d9eb8527258479805f5a8132dd9e6e3e572d8

Marking verified, lvm2 can now fallback to sync io if aio fails.


1) reduce max aio limit for easier reproducibility:

# sudo sysctl -w fs.aio-max-nr=5
fs.aio-max-nr = 5


2) create aio load in separate session:

# fio --name=randomwrite --ioengine=libaio --iodepth=1 --rw=randwrite --size=4k --numjobs=100 --runtime=1h --time_based


3) check aio number hits the limit:

# cat /proc/sys/fs/aio-nr
5


4) attempt 'vgs' command

# vgs
  Failed to set up async io, using sync io.
  VG            #PV #LV #SN Attr   VSize  VFree
  rhel_virt-371   1   2   0 wz--n- <7.00g    0



lvm2-2.02.185-2.el7.x86_64

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2019:2253