Bug 1576464

Created attachment 1433878 [details]
vbmc errors

I think this is fixed upstream by:

commit 4d7384eb9ddef2008cb0cc165eb808f74bc83d6b
Author:     Vincent Bernat <vincent>
AuthorDate: Tue Apr 10 08:27:15 2018 +0200
Commit:     Michal Privoznik <mprivozn>
CommitDate: Wed Apr 11 11:18:37 2018 +0200

    util: don't check for parallel iteration in hash-related functions
    
    This is the responsability of the caller to apply the correct lock
    before using these functions. Moreover, the use of a simple boolean
    was still racy: two threads may check the boolean and "lock" it
    simultaneously.
    
    Users of functions from src/util/virhash.c have to be checked for
    correctness. Lookups and iteration should hold a RO
    lock. Modifications should hold a RW lock.
    
    Most important uses seem to be covered. Callers have now a greater
    responsability, notably the ability to execute some operations while
    iterating were reliably forbidden before are now accepted.
    
    Signed-off-by: Vincent Bernat <vincent>

libvirt.git $ git describe --contains 4d7384eb9ddef2008cb0cc165eb808f74bc83d6b
v4.3.0-rc1~369

A reproducer would be useful.

That said, seems like something in this area was very recently fixed in upstream libvirt, in tis commit:

    4d7384e -- "util: don't check for parallel iteration in 
    hash-related functions"

But note that the above commit isn't in the libvirt version (3.9.0, package: 14.el7_5.2) running in your setup.

Maybe Michal will be able to tell us a bit more.

(In reply to Kashyap Chamarthy from comment #4)
> A reproducer would be useful.
> 
> That said, seems like something in this area was very recently fixed in
> upstream libvirt, in tis commit:
> 
>     4d7384e -- "util: don't check for parallel iteration in 
>     hash-related functions"
> 
> But note that the above commit isn't in the libvirt version (3.9.0, package:
> 14.el7_5.2) running in your setup.
> 
> Maybe Michal will be able to tell us a bit more.

Ah, Michal already pointed to the same commit in his earlier comment.  And he elaborated further on IRC:

    I think the problem is that we've switched to RW locks which allows
    multiple readers to work over list of domains (in fact a hash 
    table), however the rest of the code (hash table impl) had this
    check preventing access from multiple threads.

    For instance, if one thread is listing running VMs while the other 
    is fetching stats for all running VMs it may so happen that these
    threads will clash on the bogus check - hence the error message.

Moving to POST per comment 3.

Reproduced with libvirt-3.9.0-14.el7_5.4.x86_64.

Test steps:
1.Start a guest:
#virsh start test1

2.Do 'virsh list' in a loop:
#for i in {1..1000}; do virsh list; done

3.Open another terminal, do 'virsh domstats' in a loop:
#for i in {1..1000}; do virsh domstats; done

4.Check the libvirtd.log:
#cat /var/log/libvirt/libvirtd.log | grep -i virhash
2018-05-14 07:28:48.812+0000: 2177: error : virHashForEach:597 : Hash operation not allowed during iteration
2018-05-14 07:28:50.426+0000: 2175: error : virHashForEach:597 : Hash operation not allowed during iteration
2018-05-14 07:29:19.708+0000: 2175: error : virHashForEach:597 : Hash operation not allowed during iteration

Do you know when you will have a build available with this fix, or is it possible to get another scratch build built?  The output from the scratch build from comment no longer seems to be there.

Can not reproduce the issue with the scratch build in comment 12.

*** Bug 1571384 has been marked as a duplicate of this bug. ***

Does this bz need to be cloned for 7.5?

We would like this patch to be considered for 7.5.z.  This bug has been causing many failures of Openstack deployments that use Virtualbmc.  As shown in comments 7 and 8, this patch works well and fixes these deployment failures.

Verified with libvirt-4.3.0-1.el7.x86_64.

Test steps:
1.Start a guest:
#virsh start test1

2.Do 'virsh list' in a loop:
#for i in {1..1000}; do virsh list; done

3.Open another terminal, do 'virsh domstats' in a loop:
#for i in {1..1000}; do virsh domstats; done

4.Check the libvirtd.log after step 2&3, no error "Hash operation not allowed during iteration":
#cat /var/log/libvirt/libvirtd.log | grep -i "Hash operation not allowed during iteration"
no output

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/RHSA-2018:3113