lkml.org 
[lkml]   [2019]   [Dec]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH tip/core/rcu 01/10] rcu: Use *_ONCE() to protect lockless ->expmask accesses
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_node structure's ->expmask field is accessed locklessly when
starting a new expedited grace period and when reporting an expedited
RCU CPU stall warning. This commit therefore handles the former by
taking a snapshot of ->expmask while the lock is held and the latter
by applying READ_ONCE() to lockless reads and WRITE_ONCE() to the
corresponding updates.

Link: https://lore.kernel.org/lkml/CANpmjNNmSOagbTpffHr4=Yedckx9Rm2NuGqC9UqE+AOz5f1-ZQ@mail.gmail.com
Reported-by: syzbot+134336b86f728d6e55a0@syzkaller.appspotmail.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Marco Elver <elver@google.com>
---
kernel/rcu/tree_exp.h | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index d632cd0..69c5aa6 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -134,7 +134,7 @@ static void __maybe_unused sync_exp_reset_tree(void)
rcu_for_each_node_breadth_first(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
WARN_ON_ONCE(rnp->expmask);
- rnp->expmask = rnp->expmaskinit;
+ WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
@@ -211,7 +211,7 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp,
rnp = rnp->parent;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
WARN_ON_ONCE(!(rnp->expmask & mask));
- rnp->expmask &= ~mask;
+ WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
}
}

@@ -241,7 +241,7 @@ static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
- rnp->expmask &= ~mask;
+ WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
__rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
}

@@ -372,12 +372,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

/* IPI the remaining CPUs for expedited quiescent state. */
- for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
+ for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);

- if (!(mask_ofl_ipi & mask))
- continue;
retry_ipi:
if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
mask_ofl_test |= mask;
@@ -491,7 +489,7 @@ static void synchronize_sched_expedited_wait(void)
struct rcu_data *rdp;

mask = leaf_node_cpu_bit(rnp, cpu);
- if (!(rnp->expmask & mask))
+ if (!(READ_ONCE(rnp->expmask) & mask))
continue;
ndetected++;
rdp = per_cpu_ptr(&rcu_data, cpu);
@@ -503,7 +501,8 @@ static void synchronize_sched_expedited_wait(void)
}
pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
jiffies - jiffies_start, rcu_state.expedited_sequence,
- rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
+ READ_ONCE(rnp_root->expmask),
+ ".T"[!!rnp_root->exp_tasks]);
if (ndetected) {
pr_err("blocking rcu_node structures:");
rcu_for_each_node_breadth_first(rnp) {
@@ -513,7 +512,7 @@ static void synchronize_sched_expedited_wait(void)
continue;
pr_cont(" l=%u:%d-%d:%#lx/%c",
rnp->level, rnp->grplo, rnp->grphi,
- rnp->expmask,
+ READ_ONCE(rnp->expmask),
".T"[!!rnp->exp_tasks]);
}
pr_cont("\n");
@@ -521,7 +520,7 @@ static void synchronize_sched_expedited_wait(void)
rcu_for_each_leaf_node(rnp) {
for_each_leaf_node_possible_cpu(rnp, cpu) {
mask = leaf_node_cpu_bit(rnp, cpu);
- if (!(rnp->expmask & mask))
+ if (!(READ_ONCE(rnp->expmask) & mask))
continue;
dump_cpu_task(cpu);
}
--
2.9.5
\
 
 \ /
  Last update: 2019-12-10 05:02    [W:0.042 / U:0.592 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site