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srcu: Create concurrency-safe helper for initiating size transition 

Once there are contention-initiated size transitions, it will be
possible for rcutorture to initiate a transition at the same time
as a contention-initiated transition.  This commit therefore creates
a concurrency-safe helper function named srcu_transition_to_big() to
safely initiate size transitions.

Co-developed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-01-27 14:56:39 -08:00
parent ee5e2448bc
commit 99659f64b1
1 changed files with 21 additions and 2 deletions
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23
kernel/rcu/srcutree.c
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@ -272,6 +272,25 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/*
* Initiate an idempotent transition to SRCU_SIZE_BIG.
*/
static void srcu_transition_to_big(struct srcu_struct *ssp)
{
unsigned long flags;
/* Double-checked locking on ->srcu_size-state. */
if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL)
return;
spin_lock_irqsave_rcu_node(ssp, flags);
if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL) {
spin_unlock_irqrestore_rcu_node(ssp, flags);
return;
}
smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC);
spin_unlock_irqrestore_rcu_node(ssp, flags);
}
/*
* First-use initialization of statically allocated srcu_struct
* structure. Wiring up the combining tree is more than can be
@ -1523,8 +1542,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
}
pr_cont(" T(%ld,%ld)\n", s0, s1);
}
if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 2)
WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_ALLOC);
if (convert_to_big == 2)
srcu_transition_to_big(ssp);
}
EXPORT_SYMBOL_GPL(srcu_torture_stats_print);