From 6364dd8191d27230176ac4b1b4daaecaf4807399 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 15 Oct 2024 09:11:05 -0700 Subject: srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite() This patch adds srcu_read_lock_lite() and srcu_read_unlock_lite(), which dispense with the read-side smp_mb() but also are restricted to code regions that RCU is watching. If a given srcu_struct structure uses srcu_read_lock_lite() and srcu_read_unlock_lite(), it is not permitted to use any other SRCU read-side marker, before, during, or after. Another price of light-weight readers is heavier weight grace periods. Such readers mean that SRCU grace periods on srcu_struct structures used by light-weight readers will incur at least two calls to synchronize_rcu(). In addition, normal SRCU grace periods for light-weight-reader srcu_struct structures never auto-expedite. Note that expedited SRCU grace periods for light-weight-reader srcu_struct structures still invoke synchronize_rcu(), not synchronize_srcu_expedited(). Something about wishing to keep the IPIs down to a dull roar. The srcu_read_lock_lite() and srcu_read_unlock_lite() functions may not (repeat, *not*) be used from NMI handlers, but if this is needed, an additional flavor of SRCU reader can be added by some future commit. [ paulmck: Apply Alexei Starovoitov expediting feedback. ] [ paulmck: Apply kernel test robot feedback. ] Signed-off-by: Paul E. McKenney Tested-by: kernel test robot Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Peter Zijlstra Cc: Kent Overstreet Cc: Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker --- include/linux/srcutree.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/srcutree.h') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 79ad809c7f03..8074138cbd62 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -46,6 +46,7 @@ struct srcu_data { /* Values for ->srcu_reader_flavor. */ #define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock(). #define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe(). +#define SRCU_READ_FLAVOR_LITE 0x4 // srcu_read_lock_lite(). /* * Node in SRCU combining tree, similar in function to rcu_data. -- cgit v1.2.3