On 08/07, Trond Myklebust wrote: > > On Wed, 2007-08-08 at 01:37 +0400, Oleg Nesterov wrote: > > On 08/07, Trond Myklebust wrote: > > > > > > On Fri, 2007-08-03 at 21:21 +0400, Oleg Nesterov wrote: > > > > On 08/03, Trond Myklebust wrote: > > > > > I'll have a look at this. I suspect that most if not all of our calls > > > > > to > > > > > run_workqueue()/flush_scheduled_work() can now be replaced by more > > > > > targeted calls to cancel_work_sync() and cancel_delayed_work_sync(). > > > > > > > > Yes, please, if possible. > > > > > > All the NFS and SUNRPC cases appear to be trivial. IOW: the only reason > > > for the flush_workqueue()/flush_scheduled_work() calls was to ensure > > > that the cancel_work()/cancel_delayed_work() calls preceding them have > > > completed. Nevertheless I've split the conversion into two patches, > > > since one touches only the NFS code, whereas the other touches the > > > SUNRPC client and server code. > > > > > > The two patches have been tested, and appear to work... > > > > Great! > > > > > void > > > nfs4_kill_renewd(struct nfs_client *clp) > > > { > > > down_read(&clp->cl_sem); > > > - cancel_delayed_work(&clp->cl_renewd); > > > + cancel_delayed_work_sync(&clp->cl_renewd); > > > up_read(&clp->cl_sem); > > > - flush_scheduled_work(); > > > } > > > > this looks unsafe to me, the window is very small, but afaics this can > > deadlock if called when nfs4_renew_state() has already started, but didn't > > take ->cl_sem yet. > > Not really. We have removed the nfs_client from the public lists, and we > are guaranteed that there are no more active superblocks attached to it > so nothing can call the reclaimer routine (which is the only routine > that takes a write lock on clp->cl_sem).
Thanks for your explanation. Not that I was able to understand, nfs is a black magic to me :) But. nfs4_renew_state() checks list_empty(&clp->cl_superblocks) under clp->cl_sem? So, if it is possible that clp->cl_renewd was scheduled at the time when nfs4_kill_renewd(), we can deadlock, no? Because nfs4_renew_state() needs clp->cl_sem to complete, but nfs4_kill_renewd() holds this sem, and waits for nfs4_renew_state() completion. > > Btw, unless I missed something, the code without this patch looks incorrect > > too: cancel_delayed_work() can fail if the timer expired, but the > > ->cl_renewd > > didn't run yet. In that case nfs4_renew_state() can run and re-schedule > > itself > > after flush_scheduled_work() returns. > > No, that should not be possible. Again, see above: there are no active > superblocks, so clp->cl_superblocks is empty. Yes, thanks. I missed "goto out" in nfs4_renew_state(). Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/