From: "Paul E. McKenney" paulmck@kernel.org
This commit causes SRCU readers to use ->srcu_ctrs for counter selection instead of ->srcu_idx. This takes another step towards array-indexing-free SRCU readers.
[ paulmck: Apply kernel test robot feedback. ]
Co-developed-by: Z qiang qiang.zhang1211@gmail.com Signed-off-by: Z qiang qiang.zhang1211@gmail.com Signed-off-by: Paul E. McKenney paulmck@kernel.org Tested-by: kernel test robot oliver.sang@intel.com Cc: Alexei Starovoitov ast@kernel.org Cc: Andrii Nakryiko andrii@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Kent Overstreet kent.overstreet@linux.dev Cc: bpf@vger.kernel.org Signed-off-by: Boqun Feng boqun.feng@gmail.com --- include/linux/srcutree.h | 9 +++++---- kernel/rcu/srcutree.c | 23 +++++++++++++---------- 2 files changed, 18 insertions(+), 14 deletions(-)
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index c794d599db5c..1b01ced61a45 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -101,6 +101,7 @@ struct srcu_usage { */ struct srcu_struct { unsigned int srcu_idx; /* Current rdr array element. */ + struct srcu_ctr __percpu *srcu_ctrp; struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ struct lockdep_map dep_map; struct srcu_usage *srcu_sup; /* Update-side data. */ @@ -167,6 +168,7 @@ struct srcu_struct { #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ { \ .sda = &pcpu_name, \ + .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ }
@@ -222,13 +224,12 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); */ static inline int __srcu_read_lock_lite(struct srcu_struct *ssp) { - int idx; + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite()."); - idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */ + this_cpu_inc(scp->srcu_locks.counter); /* Y */ barrier(); /* Avoid leaking the critical section. */ - return idx; + return scp - &ssp->sda->srcu_ctrs[0]; }
/* diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d7ee2f345e19..7efde1a2344e 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -253,8 +253,10 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0); INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu); ssp->srcu_sup->sda_is_static = is_static; - if (!is_static) + if (!is_static) { ssp->sda = alloc_percpu(struct srcu_data); + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; + } if (!ssp->sda) goto err_free_sup; init_srcu_struct_data(ssp); @@ -742,12 +744,11 @@ EXPORT_SYMBOL_GPL(__srcu_check_read_flavor); */ int __srcu_read_lock(struct srcu_struct *ssp) { - int idx; + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
- idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); + this_cpu_inc(scp->srcu_locks.counter); smp_mb(); /* B */ /* Avoid leaking the critical section. */ - return idx; + return scp - &ssp->sda->srcu_ctrs[0]; } EXPORT_SYMBOL_GPL(__srcu_read_lock);
@@ -772,13 +773,12 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); */ int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) { - int idx; - struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); + struct srcu_ctr __percpu *scpp = READ_ONCE(ssp->srcu_ctrp); + struct srcu_ctr *scp = raw_cpu_ptr(scpp);
- idx = READ_ONCE(ssp->srcu_idx) & 0x1; - atomic_long_inc(&sdp->srcu_ctrs[idx].srcu_locks); + atomic_long_inc(&scp->srcu_locks); smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */ - return idx; + return scpp - &ssp->sda->srcu_ctrs[0]; } EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
@@ -1152,6 +1152,8 @@ static void srcu_flip(struct srcu_struct *ssp) smp_mb(); /* E */ /* Pairs with B and C. */
WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter. + WRITE_ONCE(ssp->srcu_ctrp, + &ssp->sda->srcu_ctrs[!(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0])]);
/* * Ensure that if the updater misses an __srcu_read_unlock() @@ -2000,6 +2002,7 @@ static int srcu_module_coming(struct module *mod) ssp->sda = alloc_percpu(struct srcu_data); if (WARN_ON_ONCE(!ssp->sda)) return -ENOMEM; + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0]; } return 0; }