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srcu: Make Tiny SRCU poll_state_synchronize_srcu() more precise

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This commit applies the more-precise grace-period-state check used by
rcu_seq_done_exact() to poll_state_synchronize_srcu().  This is important
because Tiny SRCU uses a 16-bit counter, which can wrap quite quickly.
If counter wrap continues to be a problem, then expanding ->srcu_idx
and ->srcu_idx_max to 32 bits might be warranted.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-08-02 11:59:49 -07:00
parent d66e4cf974
commit de3f2671ae
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/srcutiny.c
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@ -240,10 +240,10 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
*/ */
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
{ {
bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie); unsigned short cur_s = READ_ONCE(ssp->srcu_idx);
barrier(); barrier();
return ret; return USHORT_CMP_GE(cur_s, cookie) || USHORT_CMP_LT(cur_s, cookie - 3);
} }
EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);