On Sat Sep 19, 2026 at 1:00 AM BST, Paul E. McKenney wrote: > From: Mathieu Desnoyers <[email protected]> > > Implement a two-phase wildcard scan to guarantee forward progress of > synchronize_hazptr() even if there is a steady stream of ill-timed > readers which populate wildcards into per-CPU slots.
Hmm, I am not sure that I understand the problem here. The per-CPU slot is scanned only once per CPU, and patch 1 already introduces flipping of the overflow list. What prevents the forward progress? I think having a shared global read by all CPUs sounds really undesirable, especially that it gets flipped for each hazptr_synchronize -- this means that in the pathological case where there are a steady stream of hazptr_synchronize calls, each fast-path hazptr_acquire will have a cache miss reading hazptr_wildcard. Best, Gary > > This is performed by flipping between two wildcard values (1UL and 2UL), > and alternatively scanning for the opposite wildcard while newcoming > readers use the other one. > > There is no possibility to miss a reader because all slots for all > wildcards are accounted for during a synchronize. > > As a simplification, use this period flip to drive the hazptr overflow > list selection as well, since there is really no point is making the > overflow list flip use a different state. > > Protect the wildcard flip with a mutex. > > Signed-off-by: Mathieu Desnoyers <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Cc: Boqun Feng <[email protected]> > Reviewed-by: Bradley Morgan <[email protected]> > --- > include/linux/hazptr.h | 6 ++- > kernel/hazptr.c | 98 ++++++++++++++++++++++++++++++------------ > 2 files changed, 74 insertions(+), 30 deletions(-)
