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srcu: Make Tiny SRCU use multi-bit grace-period counter
commit 74612a07b8
upstream.
There is a need for a polling interface for SRCU grace periods. This
polling needs to distinguish between an SRCU instance being idle on the
one hand or in the middle of a grace period on the other. This commit
therefore converts the Tiny SRCU srcu_struct structure's srcu_idx from
a defacto boolean to a free-running counter, using the bottom bit to
indicate that a grace period is in progress. The second-from-bottom
bit is thus used as the index returned by srcu_read_lock().
Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
[ paulmck: Fix ->srcu_lock_nesting[] indexing per Neeraj Upadhyay. ]
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
641e1d8840
commit
450948b06c
2 changed files with 6 additions and 5 deletions
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@ -15,7 +15,7 @@
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struct srcu_struct {
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short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
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short srcu_idx; /* Current reader array element. */
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unsigned short srcu_idx; /* Current reader array element in bit 0x2. */
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u8 srcu_gp_running; /* GP workqueue running? */
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u8 srcu_gp_waiting; /* GP waiting for readers? */
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struct swait_queue_head srcu_wq;
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@ -59,7 +59,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
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{
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int idx;
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idx = READ_ONCE(ssp->srcu_idx);
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idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
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WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
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return idx;
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}
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@ -80,7 +80,7 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
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{
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int idx;
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idx = READ_ONCE(ssp->srcu_idx) & 0x1;
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idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
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pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
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tt, tf, idx,
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READ_ONCE(ssp->srcu_lock_nesting[!idx]),
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@ -124,11 +124,12 @@ void srcu_drive_gp(struct work_struct *wp)
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ssp->srcu_cb_head = NULL;
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ssp->srcu_cb_tail = &ssp->srcu_cb_head;
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local_irq_enable();
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idx = ssp->srcu_idx;
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WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
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idx = (ssp->srcu_idx & 0x2) / 2;
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WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
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WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
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swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
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WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
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WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
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/* Invoke the callbacks we removed above. */
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while (lh) {
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