libvirt users - Apr 2018 - Re: error : virHashForEach:597 : Hash operation not allowed during iteration

❦  4 avril 2018 17:00 +0200, Vincent Bernat <bernat@luffy.cx> :
>>> You can do that locally, but as a patch it's very unlikely to
be
>>> accepted upstream because we've introduced RW locks to be able
to access
>>> domain list from multiple threads.
>>
>> Looking a bit more, the whole "iterating" bit is currently
>> unsafe. First, it is racy since it's "check then take".
Two threads may
>> check the value is false and start iterating both. Moreover, at some
>> places, it is not set, for example in virHashAddOrUpdateEntry(). So, it
>> would be possible to call this function and during the update to
iterate
>> over the hash. This seems to be prevented only by callers using RW
>> lock. So, it seems we can just remove this "iterating" bool
and just
>> check all users of these functions are using the appropriate lock.
>
> My bad, I didn't see the use of table->current...
It seems it can also go away if caller correctly use a RW lock. I am
currently testing the attached patch on a few servers (patch for master,
but applied on our 3.6 version). After checking many locations, I came
to conclusion that locks are used correctly.




-- 
Use library functions.
            - The Elements of Programming Style (Kernighan & Plauger)

On 04/04/2018 08:38 PM, Vincent Bernat wrote:
> 0001-util-don-t-check-for-parallel-iteration-in-hash-rela.patch
> 
> 
> From 7bf32825325b124edce58687a8cd2ceff13328b9 Mon Sep 17 00:00:00 2001
> From: Vincent Bernat <vincent@bernat.im>
> Date: Wed, 4 Apr 2018 16:25:37 +0200
> Subject: [PATCH] util: don't check for parallel iteration in
hash-related
>  functions
Can you send this as a regular patch? I'd like to review it.

Michal

❦  5 avril 2018 17:00 +0200, Michal Privoznik <mprivozn@redhat.com> :
>> 0001-util-don-t-check-for-parallel-iteration-in-hash-rela.patch
>> 
>> 
>> From 7bf32825325b124edce58687a8cd2ceff13328b9 Mon Sep 17 00:00:00 2001
>> From: Vincent Bernat <vincent@bernat.im>
>> Date: Wed, 4 Apr 2018 16:25:37 +0200
>> Subject: [PATCH] util: don't check for parallel iteration in
hash-related
>>  functions
>
> Can you send this as a regular patch? I'd like to review it.
What do you mean by regular? Not an attachment? Through git send-email?

FI, I am now running this patch on 22 hosts without any detected issues.
-- 
Let the machine do the dirty work.
            - The Elements of Programming Style (Kernighan & Plauger)