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srcu: Prevent __call_srcu() counter wrap with read-side critical section

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Ever since cdf7abc461 ("srcu: Allow use of Tiny/Tree SRCU from
both process and interrupt context"), it has been permissible
to use SRCU read-side critical sections in interrupt context.
This allows __call_srcu() to use SRCU read-side critical sections to
prevent a new SRCU grace period from ending before the call to either
srcu_funnel_gp_start() or srcu_funnel_exp_start completes, thus preventing
SRCU grace-period counter overflow during that time.

Note that this does not permit removal of the counter-wrap checks in
srcu_gp_end().  These check are necessary to handle the case where
a given CPU does not interact at all with SRCU for an extended time
period.

This commit therefore adds an SRCU read-side critical section to
__call_srcu() in order to prevent grace period counter wrap during
the funnel-locking process.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-04-25 13:01:25 -07:00 • committed by Paul E. McKenney
parent f3e763c3e5
commit 0607ba8403
1 changed files with 3 additions and 0 deletions
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3
kernel/rcu/srcutree.c
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@ -858,6 +858,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm) rcu_callback_t func, bool do_norm)
{ {
unsigned long flags; unsigned long flags;
int idx;
bool needexp = false; bool needexp = false;
bool needgp = false; bool needgp = false;
unsigned long s; unsigned long s;
@ -871,6 +872,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
return; return;
} }
rhp->func = func; rhp->func = func;
idx = srcu_read_lock(sp);
local_irq_save(flags); local_irq_save(flags);
sdp = this_cpu_ptr(sp->sda); sdp = this_cpu_ptr(sp->sda);
spin_lock_rcu_node(sdp); spin_lock_rcu_node(sdp);
@ -892,6 +894,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
srcu_funnel_gp_start(sp, sdp, s, do_norm); srcu_funnel_gp_start(sp, sdp, s, do_norm);
else if (needexp) else if (needexp)
srcu_funnel_exp_start(sp, sdp->mynode, s); srcu_funnel_exp_start(sp, sdp->mynode, s);
srcu_read_unlock(sp, idx);
} }
/** /**