Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-11-26 06:02:05 +00:00
Code Issues Packages Projects Releases Wiki Activity

rcu: Check for jiffies going backwards

Browse Source 
A report of a 12-jiffy normal RCU CPU stall warning raises interesting
questions about the nature of time on the offending system.  This commit
instruments rcu_sched_clock_irq(), which is RCU's hook into the
scheduling-clock interrupt, checking for the jiffies counter going
backwards.

Reported-by: Saravanan D <sarvanand@fb.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-02-23 17:29:37 -08:00
parent 90d2efe7bd
commit c708b08c65
2 changed files with 11 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/rcu/tree.c
View File

@ -1679,6 +1679,8 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
WRITE_ONCE(rdp->last_sched_clock, jiffies);
WRITE_ONCE(rdp->gpwrap, false);
rcu_gpnum_ovf(rnp, rdp);
return ret;
@ -2609,6 +2611,13 @@ static void rcu_do_batch(struct rcu_data *rdp)
*/
void rcu_sched_clock_irq(int user)
{
unsigned long j;
if (IS_ENABLED(CONFIG_PROVE_RCU)) {
j = jiffies;
WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
__this_cpu_write(rcu_data.last_sched_clock, j);
}
trace_rcu_utilization(TPS("Start scheduler-tick"));
lockdep_assert_irqs_disabled();
raw_cpu_inc(rcu_data.ticks_this_gp);
@ -4179,6 +4188,7 @@ rcu_boot_init_percpu_data(int cpu)
rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
rdp->last_sched_clock = jiffies;
rdp->cpu = cpu;
rcu_boot_init_nocb_percpu_data(rdp);
}

1
kernel/rcu/tree.h
View File

@ -254,6 +254,7 @@ struct rcu_data {
unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */
short rcu_onl_gp_flags; /* ->gp_flags at last online. */
unsigned long last_fqs_resched; /* Time of last rcu_resched(). */
unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */
int cpu;
};