> is this an RT-only problem? Because mainline should not allow read->read
> locking or read->write locking for reader-writer locks. If this only
> happens on v4.18 and not on v4.19 then something must have fixed it.
Probably misunderstanding, but I'd say that read->read locking is "the
norm"...?
If you don't use qrwlock, readers are also "recursive", in part.,
P0 P1
read_lock(l)
write_lock(l)
read_lock(l)
won't block P0 on the second read_lock(). (qrwlock somehow complicate
the analysis; IIUC, they are recursive if and only if in_interrupt().).
Andrea
>
>
> Sebastian
