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authorPingfan Liu <kernelfans@gmail.com>2022-11-23 16:56:37 +0300
committerPaul E. McKenney <paulmck@kernel.org>2023-01-04 04:49:23 +0300
commit1bafbfb3e1a18af7f404977ed0d218dc4f176f8e (patch)
tree4b7457482905c85e7491dfa10b34c8d847a9e276 /kernel/rcu
parentefa3c40cfac0777071e30383d209534e09ee454b (diff)
downloadlinux-1bafbfb3e1a18af7f404977ed0d218dc4f176f8e.tar.xz
srcu: Remove needless rcu_seq_done() check while holding read lock
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>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/srcutree.c11
1 files changed, 7 insertions, 4 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 6af031200580..68b8d8b150db 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -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);