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srcu: Provide polling interfaces for Tree SRCU grace periods

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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>
This commit is contained in:
Paul E. McKenney 2020-11-13 17:31:55 -08:00
parent 8b5bd67cf6
commit 5358c9fa54
1 changed files with 63 additions and 4 deletions
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67
kernel/rcu/srcutree.c
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@ -810,7 +810,8 @@ static void srcu_leak_callback(struct rcu_head *rhp)
/*
* Start an SRCU grace period, and also queue the callback if non-NULL.
*/
static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rhp, bool do_norm)
static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
struct rcu_head *rhp, bool do_norm)
{
unsigned long flags;
int idx;
@ -819,10 +820,12 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
unsigned long s;
struct srcu_data *sdp;
check_init_srcu_struct(ssp);
idx = srcu_read_lock(ssp);
sdp = raw_cpu_ptr(ssp->sda);
spin_lock_irqsave_rcu_node(sdp, flags);
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
if (rhp)
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_gp_seq));
s = rcu_seq_snap(&ssp->srcu_gp_seq);
@ -841,6 +844,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
else if (needexp)
srcu_funnel_exp_start(ssp, sdp->mynode, s);
srcu_read_unlock(ssp, idx);
return s;
}
/*
@ -874,7 +878,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct rcu_head *rh
static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm)
{
check_init_srcu_struct(ssp);
if (debug_rcu_head_queue(rhp)) {
/* Probable double call_srcu(), so leak the callback. */
WRITE_ONCE(rhp->func, srcu_leak_callback);
@ -882,7 +885,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
return;
}
rhp->func = func;
srcu_gp_start_if_needed(ssp, rhp, do_norm);
(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
}
/**
@ -1011,6 +1014,62 @@ void synchronize_srcu(struct srcu_struct *ssp)
}
EXPORT_SYMBOL_GPL(synchronize_srcu);
/**
* get_state_synchronize_srcu - Provide an end-of-grace-period cookie
* @ssp: srcu_struct to provide cookie for.
*
* This function returns a cookie that can be passed to
* poll_state_synchronize_srcu(), which will return true if a full grace
* period has elapsed in the meantime. It is the caller's responsibility
* to make sure that grace period happens, for example, by invoking
* call_srcu() after return from get_state_synchronize_srcu().
*/
unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
{
// Any prior manipulation of SRCU-protected data must happen
// before the load from ->srcu_gp_seq.
smp_mb();
return rcu_seq_snap(&ssp->srcu_gp_seq);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
/**
* start_poll_synchronize_srcu - Provide cookie and start grace period
* @ssp: srcu_struct to provide cookie for.
*
* This function returns a cookie that can be passed to
* poll_state_synchronize_srcu(), which will return true if a full grace
* period has elapsed in the meantime. Unlike get_state_synchronize_srcu(),
* this function also ensures that any needed SRCU grace period will be
* started. This convenience does come at a cost in terms of CPU overhead.
*/
unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
{
return srcu_gp_start_if_needed(ssp, NULL, true);
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
/**
* poll_state_synchronize_srcu - Has cookie's grace period ended?
* @ssp: srcu_struct to provide cookie for.
* @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu().
*
* This function takes the cookie that was returned from either
* get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and
* returns @true if an SRCU grace period elapsed since the time that the
* cookie was created.
*/
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
{
if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie))
return false;
// Ensure that the end of the SRCU grace period happens before
// any subsequent code that the caller might execute.
smp_mb(); // ^^^
return true;
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
/*
* Callback function for srcu_barrier() use.
*/