123 lines
4.1 KiB
Diff
123 lines
4.1 KiB
Diff
|
From 5a3649e609ba5a5e6765d0a3b13a126020f03d8e Mon Sep 17 00:00:00 2001
|
||
|
|
From: Peter Zijlstra <peterz@infradead.org>
|
||
|
|
Date: Wed, 6 Jun 2018 15:31:26 +0200
|
||
|
|
Subject: [PATCH 343/365] futex: Fix pi_state->owner serialization
|
||
|
|
|
||
|
|
[ Upstream commit c74aef2d06a9f59cece89093eecc552933cba72a ]
|
||
|
|
|
||
|
|
There was a reported suspicion about a race between exit_pi_state_list()
|
||
|
|
and put_pi_state(). The same report mentioned the comment with
|
||
|
|
put_pi_state() said it should be called with hb->lock held, and it no
|
||
|
|
longer is in all places.
|
||
|
|
|
||
|
|
As it turns out, the pi_state->owner serialization is indeed broken. As per
|
||
|
|
the new rules:
|
||
|
|
|
||
|
|
734009e96d19 ("futex: Change locking rules")
|
||
|
|
|
||
|
|
pi_state->owner should be serialized by pi_state->pi_mutex.wait_lock.
|
||
|
|
For the sites setting pi_state->owner we already hold wait_lock (where
|
||
|
|
required) but exit_pi_state_list() and put_pi_state() were not and
|
||
|
|
raced on clearing it.
|
||
|
|
|
||
|
|
Fixes: 734009e96d19 ("futex: Change locking rules")
|
||
|
|
Reported-by: Gratian Crisan <gratian.crisan@ni.com>
|
||
|
|
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
|
||
|
|
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
||
|
|
Cc: dvhart@infradead.org
|
||
|
|
Cc: stable@vger.kernel.org
|
||
|
|
Link: https://lkml.kernel.org/r/20170922154806.jd3ffltfk24m4o4y@hirez.programming.kicks-ass.net
|
||
|
|
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
||
|
|
Signed-off-by: Julia Cartwright <julia@ni.com>
|
||
|
|
---
|
||
|
|
kernel/futex.c | 34 ++++++++++++++++++++++------------
|
||
|
|
1 file changed, 22 insertions(+), 12 deletions(-)
|
||
|
|
|
||
|
|
diff --git a/kernel/futex.c b/kernel/futex.c
|
||
|
|
index 8df43644f88d..8b01a19e3260 100644
|
||
|
|
--- a/kernel/futex.c
|
||
|
|
+++ b/kernel/futex.c
|
||
|
|
@@ -836,8 +836,6 @@ static void get_pi_state(struct futex_pi_state *pi_state)
|
||
|
|
/*
|
||
|
|
* Drops a reference to the pi_state object and frees or caches it
|
||
|
|
* when the last reference is gone.
|
||
|
|
- *
|
||
|
|
- * Must be called with the hb lock held.
|
||
|
|
*/
|
||
|
|
static void put_pi_state(struct futex_pi_state *pi_state)
|
||
|
|
{
|
||
|
|
@@ -852,16 +850,22 @@ static void put_pi_state(struct futex_pi_state *pi_state)
|
||
|
|
* and has cleaned up the pi_state already
|
||
|
|
*/
|
||
|
|
if (pi_state->owner) {
|
||
|
|
- raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
||
|
|
- list_del_init(&pi_state->list);
|
||
|
|
- raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
||
|
|
+ struct task_struct *owner;
|
||
|
|
|
||
|
|
- rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
|
||
|
|
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
||
|
|
+ owner = pi_state->owner;
|
||
|
|
+ if (owner) {
|
||
|
|
+ raw_spin_lock(&owner->pi_lock);
|
||
|
|
+ list_del_init(&pi_state->list);
|
||
|
|
+ raw_spin_unlock(&owner->pi_lock);
|
||
|
|
+ }
|
||
|
|
+ rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
|
||
|
|
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
||
|
|
}
|
||
|
|
|
||
|
|
- if (current->pi_state_cache)
|
||
|
|
+ if (current->pi_state_cache) {
|
||
|
|
kfree(pi_state);
|
||
|
|
- else {
|
||
|
|
+ } else {
|
||
|
|
/*
|
||
|
|
* pi_state->list is already empty.
|
||
|
|
* clear pi_state->owner.
|
||
|
|
@@ -920,14 +924,15 @@ void exit_pi_state_list(struct task_struct *curr)
|
||
|
|
raw_spin_unlock_irq(&curr->pi_lock);
|
||
|
|
|
||
|
|
spin_lock(&hb->lock);
|
||
|
|
-
|
||
|
|
- raw_spin_lock_irq(&curr->pi_lock);
|
||
|
|
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
||
|
|
+ raw_spin_lock(&curr->pi_lock);
|
||
|
|
/*
|
||
|
|
* We dropped the pi-lock, so re-check whether this
|
||
|
|
* task still owns the PI-state:
|
||
|
|
*/
|
||
|
|
if (head->next != next) {
|
||
|
|
- raw_spin_unlock_irq(&curr->pi_lock);
|
||
|
|
+ raw_spin_unlock(&curr->pi_lock);
|
||
|
|
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
||
|
|
spin_unlock(&hb->lock);
|
||
|
|
raw_spin_lock_irq(&curr->pi_lock);
|
||
|
|
continue;
|
||
|
|
@@ -937,9 +942,10 @@ void exit_pi_state_list(struct task_struct *curr)
|
||
|
|
WARN_ON(list_empty(&pi_state->list));
|
||
|
|
list_del_init(&pi_state->list);
|
||
|
|
pi_state->owner = NULL;
|
||
|
|
- raw_spin_unlock_irq(&curr->pi_lock);
|
||
|
|
+ raw_spin_unlock(&curr->pi_lock);
|
||
|
|
|
||
|
|
get_pi_state(pi_state);
|
||
|
|
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
||
|
|
spin_unlock(&hb->lock);
|
||
|
|
|
||
|
|
rt_mutex_futex_unlock(&pi_state->pi_mutex);
|
||
|
|
@@ -1221,6 +1227,10 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
|
||
|
|
|
||
|
|
WARN_ON(!list_empty(&pi_state->list));
|
||
|
|
list_add(&pi_state->list, &p->pi_state_list);
|
||
|
|
+ /*
|
||
|
|
+ * Assignment without holding pi_state->pi_mutex.wait_lock is safe
|
||
|
|
+ * because there is no concurrency as the object is not published yet.
|
||
|
|
+ */
|
||
|
|
pi_state->owner = p;
|
||
|
|
raw_spin_unlock_irq(&p->pi_lock);
|
||
|
|
|
||
|
|
--
|
||
|
|
2.28.0
|
||
|
|
|