From: Paul E. McKenney paulmck@kernel.org
commit 29d2bb94a8a126ce80ffbb433b648b32fdea524e upstream.
There is a need for a polling interface for SRCU grace periods. This polling needs to initiate an SRCU grace period without having to queue (and manage) a callback. This commit therefore splits the Tree SRCU __call_srcu() function into callback-initialization and queuing/start-grace-period portions, with the latter in a new function named srcu_gp_start_if_needed(). This function may be passed a NULL callback pointer, in which case it will refrain from queuing anything.
Why have the new function mess with queuing? Locking considerations, of course!
Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ Reported-by: Kent Overstreet kent.overstreet@gmail.com 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 --- kernel/rcu/srcutree.c | 66 ++++++++++++++++++++++++++++---------------------- 1 file changed, 37 insertions(+), 29 deletions(-)
--- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -809,6 +809,42 @@ static void srcu_leak_callback(struct rc }
/* + * 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) +{ + unsigned long flags; + int idx; + bool needexp = false; + bool needgp = false; + unsigned long s; + struct srcu_data *sdp; + + 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); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_gp_seq)); + s = rcu_seq_snap(&ssp->srcu_gp_seq); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { + sdp->srcu_gp_seq_needed = s; + needgp = true; + } + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { + sdp->srcu_gp_seq_needed_exp = s; + needexp = true; + } + spin_unlock_irqrestore_rcu_node(sdp, flags); + if (needgp) + srcu_funnel_gp_start(ssp, sdp, s, do_norm); + else if (needexp) + srcu_funnel_exp_start(ssp, sdp->mynode, s); + srcu_read_unlock(ssp, idx); +} + +/* * Enqueue an SRCU callback on the srcu_data structure associated with * the current CPU and the specified srcu_struct structure, initiating * grace-period processing if it is not already running. @@ -839,13 +875,6 @@ static void srcu_leak_callback(struct rc static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { - unsigned long flags; - int idx; - bool needexp = false; - bool needgp = false; - unsigned long s; - struct srcu_data *sdp; - check_init_srcu_struct(ssp); if (debug_rcu_head_queue(rhp)) { /* Probable double call_srcu(), so leak the callback. */ @@ -854,28 +883,7 @@ static void __call_srcu(struct srcu_stru return; } rhp->func = func; - 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); - rcu_segcblist_advance(&sdp->srcu_cblist, - rcu_seq_current(&ssp->srcu_gp_seq)); - s = rcu_seq_snap(&ssp->srcu_gp_seq); - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); - if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { - sdp->srcu_gp_seq_needed = s; - needgp = true; - } - if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { - sdp->srcu_gp_seq_needed_exp = s; - needexp = true; - } - spin_unlock_irqrestore_rcu_node(sdp, flags); - if (needgp) - srcu_funnel_gp_start(ssp, sdp, s, do_norm); - else if (needexp) - srcu_funnel_exp_start(ssp, sdp->mynode, s); - srcu_read_unlock(ssp, idx); + srcu_gp_start_if_needed(ssp, rhp, do_norm); }
/**