6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Benjamin Segall <bsegall@xxxxxxxxxx>
[ Upstream commit b5413156bad91dc2995a5c4eab1b05e56914638a ]
When cloning a new thread, its posix_cputimers are not inherited, and
are cleared by posix_cputimers_init(). However, this does not clear the
tick dependency it creates in tsk->tick_dep_mask, and the handler does
not reach the code to clear the dependency if there were no timers to
begin with.
Thus if a thread has a cputimer running before clone/fork, all
descendants will prevent nohz_full unless they create a cputimer of
their own.
Fix this by entirely clearing the tick_dep_mask in copy_process().
(There is currently no inherited state that needs a tick dependency)
Process-wide timers do not have this problem because fork does not copy
signal_struct as a baseline, it creates one from scratch.
Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model")
Signed-off-by: Ben Segall <bsegall@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/tick.h | 8 ++++++++
kernel/fork.c | 2 ++
2 files changed, 10 insertions(+)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 9459fef5b8573..9701c571a5cfe 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -252,12 +252,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
if (tick_nohz_full_enabled())
tick_nohz_dep_set_task(tsk, bit);
}
+
static inline void tick_dep_clear_task(struct task_struct *tsk,
enum tick_dep_bits bit)
{
if (tick_nohz_full_enabled())
tick_nohz_dep_clear_task(tsk, bit);
}
+
+static inline void tick_dep_init_task(struct task_struct *tsk)
+{
+ atomic_set(&tsk->tick_dep_mask, 0);
+}
+
static inline void tick_dep_set_signal(struct task_struct *tsk,
enum tick_dep_bits bit)
{
@@ -291,6 +298,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
enum tick_dep_bits bit) { }
static inline void tick_dep_clear_task(struct task_struct *tsk,
enum tick_dep_bits bit) { }
+static inline void tick_dep_init_task(struct task_struct *tsk) { }
static inline void tick_dep_set_signal(struct task_struct *tsk,
enum tick_dep_bits bit) { }
static inline void tick_dep_clear_signal(struct signal_struct *signal,
diff --git a/kernel/fork.c b/kernel/fork.c
index 9098284720e38..23efaa2c42e4f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -99,6 +99,7 @@
#include <linux/stackprotector.h>
#include <linux/user_events.h>
#include <linux/iommu.h>
+#include <linux/tick.h>
#include <asm/pgalloc.h>
#include <linux/uaccess.h>
@@ -2418,6 +2419,7 @@ __latent_entropy struct task_struct *copy_process(
acct_clear_integrals(p);
posix_cputimers_init(&p->posix_cputimers);
+ tick_dep_init_task(p);
p->io_context = NULL;
audit_set_context(p, NULL);
--
2.43.0
