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| author | Pingfan Liu <kernelfans@gmail.com> | 2022-11-23 16:56:37 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2023-01-04 04:49:23 +0300 |
| commit | 1bafbfb3e1a18af7f404977ed0d218dc4f176f8e (patch) | |
| tree | 4b7457482905c85e7491dfa10b34c8d847a9e276 /kernel/rcu | |
| parent | efa3c40cfac0777071e30383d209534e09ee454b (diff) | |
| download | linux-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.c | 11 |
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); |