Re: [PATCH] util: don't check for parallel iteration in hash-related functions

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On 04/06/2018 09:56 AM, Vincent Bernat wrote:
> 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.
> ---
>  src/util/virhash.c  | 37 ----------------------
>  tests/virhashtest.c | 75 ---------------------------------------------
>  2 files changed, 112 deletions(-)

So I went through all callbacks (even transitive ones) and I've found
two problems:

umlProcessAutoDestroyRun -> umlProcessAutoDestroyDom -> virHashRemoveEntry

qemuDomainSnapshotDiscardAllMetadata -> qemuDomainSnapshotDiscardAll ->
qemuDomainSnapshotDiscard -> virDomainSnapshotObjListRemove ->
virHashRemoveEntry

While me (and probably Peter :-)) don't care about the first one, the
second one is a real issue. I guess we need to fix that one before this
can be merged.

On a positive side, I haven't spotted any other problem. So once qemu
(and possibly uml) are fixed this can be merged as is.

Michal

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