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srcu: Remove needless rcu_seq_done() check while holding read lock

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The srcu_gp_start_if_needed() function now read-holds the srcu_struct
whose grace period is being started, which means that the corresponding
SRCU grace period cannot end.  This in turn means that the SRCU
grace-period sequence number returned by rcu_seq_snap() cannot expire
during this time.  And that means that the calls to rcu_seq_done() in
srcu_funnel_exp_start() and srcu_funnel_gp_start() can never return true.

This commit therefore removes these rcu_seq_done() checks, but adds checks
in kernels built with CONFIG_PROVE_RCU=y that splats if rcu_seq_done()
does somehow return true.

[ paulmck: Rearrange checks to handle kernels built with lockdep. ]

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: rcu@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Pingfan Liu 2022-11-23 21:56:37 +08:00 committed by Paul E. McKenney
parent efa3c40cfa
commit 1bafbfb3e1
1 changed files with 7 additions and 4 deletions
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11
kernel/rcu/srcutree.c
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@ -915,7 +915,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
if (snp)
for (; snp != NULL; snp = snp->srcu_parent) {
sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp);
if (rcu_seq_done(&ssp->srcu_gp_seq, s) ||
if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) ||
(!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)))
return;
spin_lock_irqsave_rcu_node(snp, flags);
@ -942,6 +942,9 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
*
* Note that this function also does the work of srcu_funnel_exp_start(),
* in some cases by directly invoking it.
*
* The srcu read lock should be hold around this function. And s is a seq snap
* after holding that lock.
*/
static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
unsigned long s, bool do_norm)
@ -962,7 +965,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
if (snp_leaf)
/* Each pass through the loop does one level of the srcu_node tree. */
for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != snp_leaf)
if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) && snp != snp_leaf)
return; /* GP already done and CBs recorded. */
spin_lock_irqsave_rcu_node(snp, flags);
snp_seq = snp->srcu_have_cbs[idx];
@ -999,8 +1002,8 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
/* If grace period not already done and none in progress, start it. */
if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&
/* If grace period not already in progress, start it. */
if (!WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) &&
rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
srcu_gp_start(ssp);