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Re: [libvirt] [PATCH 1/2] storage: Resolve storage driver crash



On Tue, 2017-11-07 at 08:43 -0500, John Ferlan wrote:
> 
> On 11/07/2017 04:18 AM, Cedric Bosdonnat wrote:
> > On Mon, 2017-11-06 at 15:53 -0500, John Ferlan wrote:
> > > Resolve a storage driver crash as a result of a long running
> > > storageVolCreateXML when the virStorageVolPoolRefreshThread is
> > > run as a result of a storageVolUpload complete and ran the
> > > virStoragePoolObjClearVols without checking if the creation
> > > code was currently processing a buildVol after incrementing
> > > the driver->asyncjob count.
> > > 
> > > The refreshThread needs to wait until all creation threads
> > > are completed so as to not alter the volume list while the
> > > volume is being built.
> > > 
> > > Crash from valgrind is as follows (with a bit of editing):
> > > 
> > > ==21309== Invalid read of size 8
> > > ==21309==    at 0x153E47AF: storageBackendUpdateVolTargetInfo
> > > ==21309==    by 0x153E4C30: virStorageBackendUpdateVolInfo
> > > ==21309==    by 0x153E52DE: virStorageBackendVolRefreshLocal
> > > ==21309==    by 0x153DE29E: storageVolCreateXML
> > > ==21309==    by 0x562035B: virStorageVolCreateXML
> > > ==21309==    by 0x147366: remoteDispatchStorageVolCreateXML
> > > ...
> > > ==21309==  Address 0x2590a720 is 64 bytes inside a block of size 336 free'd
> > > ==21309==    at 0x4C2F2BB: free
> > > ==21309==    by 0x54CB9FA: virFree
> > > ==21309==    by 0x55BC800: virStorageVolDefFree
> > > ==21309==    by 0x55BF1D8: virStoragePoolObjClearVols
> > > ==21309==    by 0x153D967E: virStorageVolPoolRefreshThread
> > > ...
> > > ==21309==  Block was alloc'd at
> > > ==21309==    at 0x4C300A5: calloc
> > > ==21309==    by 0x54CB483: virAlloc
> > > ==21309==    by 0x55BDC1F: virStorageVolDefParseXML
> > > ==21309==    by 0x55BDC1F: virStorageVolDefParseNode
> > > ==21309==    by 0x55BE5A4: virStorageVolDefParse
> > > ==21309==    by 0x153DDFF1: storageVolCreateXML
> > > ==21309==    by 0x562035B: virStorageVolCreateXML
> > > ==21309==    by 0x147366: remoteDispatchStorageVolCreateXML
> > > ...
> > > 
> > > Signed-off-by: John Ferlan <jferlan redhat com>
> > > ---
> > >  src/storage/storage_driver.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
> > > index b0edf9f885..5e920fc14c 100644
> > > --- a/src/storage/storage_driver.c
> > > +++ b/src/storage/storage_driver.c
> > > @@ -2257,6 +2257,7 @@ virStorageVolPoolRefreshThread(void *opaque)
> > >      virStorageBackendPtr backend;
> > >      virObjectEventPtr event = NULL;
> > >  
> > > + retry:
> > >      storageDriverLock();
> > >      if (cbdata->vol_path) {
> > >          if (virStorageBackendPloopRestoreDesc(cbdata->vol_path) < 0)
> > > @@ -2270,6 +2271,14 @@ virStorageVolPoolRefreshThread(void *opaque)
> > >      if (!(backend = virStorageBackendForType(def->type)))
> > >          goto cleanup;
> > >  
> > > +    /* Some thread is creating a new volume in the pool, we need to retry */
> > > +    if (virStoragePoolObjGetAsyncjobs(obj) > 0) {
> > > +        virStoragePoolObjUnlock(obj);
> > > +        storageDriverUnlock();
> > > +        usleep(100 * 1000);
> > > +        goto retry;
> > > +    }
> > > +
> > >      virStoragePoolObjClearVols(obj);
> > >      if (backend->refreshPool(NULL, obj) < 0)
> > >          VIR_DEBUG("Failed to refresh storage pool");
> > 
> > ACK, does the job here. I'm rather surprised to see you implementing it
> > with sleep, while you pointed me towards virCondWait yesterday. But using
> > sleep is a way less intrusive change.
> > 
> 
> Well you only asked about an alternative mechanism and condition
> variable was the first thing that popped into my mind; however, as I got
> to actually doing more thinking about it - asyncjobs is not blocking
> multiple creates from occurring; whereas, a condition variable would be
> waiting for one thing to complete.
> 
> My response to Jan also lists 2 other alternatives. This was just the
> "easiest" of the 3.  If there's other ideas, I'm open to suggestions.
> 
It looks fine to me, I was just surprised to see the sleep version ;)

--
Cedric


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