[PATCH v2 0/5] nfsd: don't allow concurrent queueing of workqueue jobs

[Jeff Layton]

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.

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
their earlier patch (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>
---
Changes in v2:
- added patche to handle rpc_call_async() errors
- rename NFSD4_CALLBACK_RESTART to NFSD4_CALLBACK_REQUEUE
- add patch to replace CB_GETATTR_BUSY with NFSD4_CALLBACK_REQUEUE
- Link to v1: https://lore.kernel.org/r/20250218-nfsd-callback-v1-0-14f966967dd8@xxxxxxxxxx

---
Jeff Layton (5):
      nfsd: prevent callback tasks running concurrently
      nfsd: eliminate cl_ra_cblist and NFSD4_CLIENT_CB_RECALL_ANY
      nfsd: replace CB_GETATTR_BUSY with NFSD4_CALLBACK_RUNNING
      nfsd: move cb_need_restart flag into cb_flags
      nfsd: handle errors from rpc_call_async()

 fs/nfsd/nfs4callback.c | 26 +++++++++++++++++---------
 fs/nfsd/nfs4layouts.c  |  7 ++++---
 fs/nfsd/nfs4proc.c     |  2 +-
 fs/nfsd/nfs4state.c    | 31 ++++++++++++++-----------------
 fs/nfsd/state.h        | 18 +++++++++++-------
 fs/nfsd/trace.h        |  2 +-
 6 files changed, 48 insertions(+), 38 deletions(-)
---
base-commit: b7e85fd7c8964e31f8fa1cf7333b12f442b642f1
change-id: 20250218-nfsd-callback-f723b8498c78

Best regards,
-- 
Jeff Layton <jlayton@xxxxxxxxxx>