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srcu: Provide polling interfaces for Tiny SRCU grace periods
commit 8b5bd67cf6
upstream.
There is a need for a polling interface for SRCU grace
periods, so this commit supplies get_state_synchronize_srcu(),
start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this
purpose. The first can be used if future grace periods are inevitable
(perhaps due to a later call_srcu() invocation), the second if future
grace periods might not otherwise happen, and the third to check if a
grace period has elapsed since the corresponding call to either of the
first two.
As with get_state_synchronize_rcu() and cond_synchronize_rcu(),
the return value from either get_state_synchronize_srcu() or
start_poll_synchronize_srcu() must be passed in to a later call to
poll_state_synchronize_srcu().
Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
[ paulmck: Add EXPORT_SYMBOL_GPL() per kernel test robot feedback. ]
[ paulmck: Apply feedback from Neeraj Upadhyay. ]
Link: https://lore.kernel.org/lkml/20201117004017.GA7444@paulmck-ThinkPad-P72/
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
450948b06c
commit
b6ae385407
4 changed files with 59 additions and 2 deletions
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@ -33,6 +33,8 @@
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#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
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#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
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#define ulong2long(a) (*(long *)(&(a)))
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#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
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#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
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/* Exported common interfaces */
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void call_rcu(struct rcu_head *head, rcu_callback_t func);
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@ -60,6 +60,9 @@ void cleanup_srcu_struct(struct srcu_struct *ssp);
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int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
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void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
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void synchronize_srcu(struct srcu_struct *ssp);
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unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
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unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
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bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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@ -16,6 +16,7 @@
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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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unsigned short srcu_idx; /* Current reader array element in bit 0x2. */
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unsigned short srcu_idx_max; /* Furthest future srcu_idx request. */
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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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@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp)
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ssp->srcu_gp_running = false;
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ssp->srcu_gp_waiting = false;
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ssp->srcu_idx = 0;
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ssp->srcu_idx_max = 0;
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INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
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INIT_LIST_HEAD(&ssp->srcu_work.entry);
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return 0;
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@ -84,6 +85,8 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
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WARN_ON(ssp->srcu_gp_waiting);
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WARN_ON(ssp->srcu_cb_head);
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WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
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WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
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WARN_ON(ssp->srcu_idx & 0x1);
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}
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EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
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@ -114,7 +117,7 @@ void srcu_drive_gp(struct work_struct *wp)
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struct srcu_struct *ssp;
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ssp = container_of(wp, struct srcu_struct, srcu_work);
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if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
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if (ssp->srcu_gp_running || USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
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return; /* Already running or nothing to do. */
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/* Remove recently arrived callbacks and wait for readers. */
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@ -147,13 +150,19 @@ void srcu_drive_gp(struct work_struct *wp)
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* straighten that out.
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*/
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WRITE_ONCE(ssp->srcu_gp_running, false);
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if (READ_ONCE(ssp->srcu_cb_head))
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if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
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schedule_work(&ssp->srcu_work);
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}
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EXPORT_SYMBOL_GPL(srcu_drive_gp);
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static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
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{
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unsigned short cookie;
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cookie = get_state_synchronize_srcu(ssp);
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if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
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return;
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WRITE_ONCE(ssp->srcu_idx_max, cookie);
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if (!READ_ONCE(ssp->srcu_gp_running)) {
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if (likely(srcu_init_done))
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schedule_work(&ssp->srcu_work);
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@ -196,6 +205,48 @@ void synchronize_srcu(struct srcu_struct *ssp)
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}
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EXPORT_SYMBOL_GPL(synchronize_srcu);
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/*
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* get_state_synchronize_srcu - Provide an end-of-grace-period cookie
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*/
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unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
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{
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unsigned long ret;
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barrier();
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ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
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barrier();
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return ret & USHRT_MAX;
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}
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EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
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/*
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* start_poll_synchronize_srcu - Provide cookie and start grace period
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*
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* The difference between this and get_state_synchronize_srcu() is that
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* this function ensures that the poll_state_synchronize_srcu() will
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* eventually return the value true.
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*/
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unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
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{
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unsigned long ret = get_state_synchronize_srcu(ssp);
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srcu_gp_start_if_needed(ssp);
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return ret;
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}
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EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
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/*
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* poll_state_synchronize_srcu - Has cookie's grace period ended?
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*/
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bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
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{
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bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie);
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barrier();
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return ret;
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}
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EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
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/* Lockdep diagnostics. */
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void __init rcu_scheduler_starting(void)
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{
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