On Sun Sep 27, 2026 at 5:51 PM CEST, Mathieu Desnoyers wrote: > Introduce a "try acquire" hazard pointer fast path, which performs an > early load of the address to store it into the hazard pointer slot, and > then re-loads that address after a barrier to check whether it has > changed meanwhile. > > On comparison failure, rather than re-try, guarantee forward progress by > falling back to the __hazptr_acquire slow path on failure. > > The acquire slow path attempts a try-acquire for any available per-CPU > slot. If that fails, it chains the backup slot into the overflow list, > therefore guaranteeing forward progress for both hazard pointer > read-side and synchronize: > > - Readers set the wildcard, and then proceed to set the more > specific address to replace the wildcard. > > - One synchronize alternates between two overflow list periods, > scanning each one while readers are added to the other period, > thus preventing a steady flow of readers from preventing > synchronize forward progress. > > With this change, the scan on per-CPU slots don't need to expect a > wildcard anymore, because none can be produced by readers. Wildcards are > only expected within overflow lists. > > Signed-off-by: Mathieu Desnoyers <[email protected]>
Suggested-by: Gary Guo <[email protected]> Link: https://lore.kernel.org/lkmm/[email protected]/ Reviewed-by: Gary Guo <[email protected]> > Cc: Paul E. McKenney <[email protected]> > Cc: Boqun Feng <[email protected]> > Cc: Bradley Morgan <[email protected]> > Cc: Gary Guo <[email protected]> > Cc: <[email protected]> > Cc: <[email protected]> > --- > include/linux/hazptr.h | 47 +++++++++++-------- > kernel/hazptr.c | 103 ++++++++++++++++++++--------------------- > 2 files changed, 76 insertions(+), 74 deletions(-)
