> On Nov 16, 2023, at 12:11 PM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote: > > I ran into this old problem again recently, last discussed here: > https://lore.kernel.org/linux-nfs/F738DB31-B527-4048-94A7-DBF00533F8C1@xxxxxxxxxx/#t > > Problem is that clients can easily issue enough WRITEs that end up in > > __break_lease > xfs_break_leased_layouts > ... > nfsd_vfs_write > ... > svc_process > svc_recv > nfsd > > .. so that all the knfsds are there, and nothing can process the > LAYOUTRETURN. > > I'm pretty sure we can make the linux client a bit smarter about it (I saw > one LAYOUTGET and one conflicting WRITE in the same TCP segment, in that > order). > > But what can knfsd do to defend itself? If nfsd threads are waiting indefinitely, that's a potential DoS vector. Ideally the thread should preserve the waiting request somehow (or return NFS4ERR_DELAY, maybe?). At some later point when the lease conflict is resolved, the requests can be reprocessed. That's my naive 800,000 ft view. -- Chuck Lever
