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srcu: Convert ->srcu_lock_count and ->srcu_unlock_count to atomic

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NMI-safe variants of srcu_read_lock() and srcu_read_unlock() are needed
by printk(), which on many architectures entails read-modify-write
atomic operations.  This commit prepares Tree SRCU for this change by
making both ->srcu_lock_count and ->srcu_unlock_count by atomic_long_t.

[ paulmck: Apply feedback from John Ogness. ]

Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Paul E. McKenney 2022-09-15 12:09:30 -07:00
parent 9abf2313ad
commit 5d0f5953b6
2 changed files with 14 additions and 14 deletions
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4
include/linux/srcutree.h
View file

@ -23,8 +23,8 @@ struct srcu_struct;
*/
struct srcu_data {
/* Read-side state. */
unsigned long srcu_lock_count[2]; /* Locks per CPU. */
unsigned long srcu_unlock_count[2]; /* Unlocks per CPU. */
atomic_long_t srcu_lock_count[2]; /* Locks per CPU. */
atomic_long_t srcu_unlock_count[2]; /* Unlocks per CPU. */
/* Update-side state. */
spinlock_t __private lock ____cacheline_internodealigned_in_smp;

24
kernel/rcu/srcutree.c
View file

@ -417,7 +417,7 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx)
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += READ_ONCE(cpuc->srcu_lock_count[idx]);
sum += atomic_long_read(&cpuc->srcu_lock_count[idx]);
}
return sum;
}
@ -434,7 +434,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += READ_ONCE(cpuc->srcu_unlock_count[idx]);
sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]);
}
return sum;
}
@ -503,10 +503,10 @@ static bool srcu_readers_active(struct srcu_struct *ssp)
for_each_possible_cpu(cpu) {
struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu);
sum += READ_ONCE(cpuc->srcu_lock_count[0]);
sum += READ_ONCE(cpuc->srcu_lock_count[1]);
sum -= READ_ONCE(cpuc->srcu_unlock_count[0]);
sum -= READ_ONCE(cpuc->srcu_unlock_count[1]);
sum += atomic_long_read(&cpuc->srcu_lock_count[0]);
sum += atomic_long_read(&cpuc->srcu_lock_count[1]);
sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]);
sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]);
}
return sum;
}
@ -636,7 +636,7 @@ int __srcu_read_lock(struct srcu_struct *ssp)
int idx;
idx = READ_ONCE(ssp->srcu_idx) & 0x1;
this_cpu_inc(ssp->sda->srcu_lock_count[idx]);
this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
smp_mb(); /* B */ /* Avoid leaking the critical section. */
return idx;
}
@ -650,7 +650,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock);
void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
{
smp_mb(); /* C */ /* Avoid leaking the critical section. */
this_cpu_inc(ssp->sda->srcu_unlock_count[idx]);
this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
@ -1687,8 +1687,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
struct srcu_data *sdp;
sdp = per_cpu_ptr(ssp->sda, cpu);
u0 = data_race(sdp->srcu_unlock_count[!idx]);
u1 = data_race(sdp->srcu_unlock_count[idx]);
u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx]));
u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx]));
/*
* Make sure that a lock is always counted if the corresponding
@ -1696,8 +1696,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
*/
smp_rmb();
l0 = data_race(sdp->srcu_lock_count[!idx]);
l1 = data_race(sdp->srcu_lock_count[idx]);
l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx]));
l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx]));
c0 = l0 - u0;
c1 = l1 - u1;