On Wed, 19 Feb 2025, Jeff Layton wrote: > While looking at the problem that Li Lingfeng reported [1] around > callback queueing failures, I noticed that there were potential > scenarios where the callback workqueue jobs could run concurrently with > an rpc_task. Since they touch some of the same fields, this is incorrect > at best and potentially dangerous. If the problem is that workqueue jobs might run concurrently with rpc_tasks and that we don't want that, could we simply run all the cb tasks as "sync" rpc tasks in the workqueue?? i.e. change rpc_call_async() in nfsd4_run_cb_work() to rpc_call_sync ... and fix any breakage because I doubt it is really as simple as that. This would fully serialise all the callbacks. Is that what to goal is here, or is the goal more subtle? Thanks, NeilBrown > > This patchset adds a new mechanism for ensuring that the same > nfsd4_callback can't run concurrently with itself, regardless of where > it is in its execution. This also gives us a more sure mechanism for > handling the places where we need to take and hold a reference on an > object while the callback is running. > > This should also fix the problem that Li Lingfeng reported, since > queueing the work from nfsd4_cb_release() should never fail. Note that > the patch they sent earlier (fdf5c9413ea) should be dropped from > nfsd-testing before this will apply cleanly. > > [1]: https://lore.kernel.org/linux-nfs/20250218135423.1487309-1-lilingfeng3@xxxxxxxxxx/ > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > --- > Jeff Layton (3): > nfsd: prevent callback tasks running concurrently > nfsd: eliminate cl_ra_cblist and NFSD4_CLIENT_CB_RECALL_ANY > nfsd: move cb_need_restart flag into cb_flags > > fs/nfsd/nfs4callback.c | 12 ++++++------ > fs/nfsd/nfs4layouts.c | 7 ++++--- > fs/nfsd/nfs4proc.c | 2 +- > fs/nfsd/nfs4state.c | 26 +++++++++++--------------- > fs/nfsd/state.h | 13 ++++++++++--- > fs/nfsd/trace.h | 2 +- > 6 files changed, 33 insertions(+), 29 deletions(-) > --- > base-commit: 4a52e5e49d1b50fcb584e434cced6d0547ddea42 > change-id: 20250218-nfsd-callback-f723b8498c78 > > Best regards, > -- > Jeff Layton <jlayton@xxxxxxxxxx> > >
