[tip: core/rcu] srcu: Apply *_ONCE() to ->srcu_last_gp_end

From: tip-bot2 for Paul E. McKenney
Date: Sat Jan 25 2020 - 05:46:59 EST


The following commit has been merged into the core/rcu branch of tip:

Commit-ID: 844a378de3372c923909681706d62336d702531e
Gitweb: https://git.kernel.org/tip/844a378de3372c923909681706d62336d702531e
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate: Mon, 04 Nov 2019 08:08:30 -08:00
Committer: Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Fri, 24 Jan 2020 10:33:51 -08:00

srcu: Apply *_ONCE() to ->srcu_last_gp_end

The ->srcu_last_gp_end field is accessed from any CPU at any time
by synchronize_srcu(), so non-initialization references need to use
READ_ONCE() and WRITE_ONCE(). This commit therefore makes that change.

Reported-by: syzbot+08f3e9d26e5541e1ecf2@xxxxxxxxxxxxxxxxxxxxxxxxx
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
kernel/rcu/srcutree.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 5dffade..21acdff 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -530,7 +530,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
idx = rcu_seq_state(ssp->srcu_gp_seq);
WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
cbdelay = srcu_get_delay(ssp);
- ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
+ WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns());
rcu_seq_end(&ssp->srcu_gp_seq);
gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))
@@ -762,6 +762,7 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp)
unsigned long flags;
struct srcu_data *sdp;
unsigned long t;
+ unsigned long tlast;

/* If the local srcu_data structure has callbacks, not idle. */
local_irq_save(flags);
@@ -780,9 +781,9 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp)

/* First, see if enough time has passed since the last GP. */
t = ktime_get_mono_fast_ns();
+ tlast = READ_ONCE(ssp->srcu_last_gp_end);
if (exp_holdoff == 0 ||
- time_in_range_open(t, ssp->srcu_last_gp_end,
- ssp->srcu_last_gp_end + exp_holdoff))
+ time_in_range_open(t, tlast, tlast + exp_holdoff))
return false; /* Too soon after last GP. */

/* Next, check for probable idleness. */