From: Julia Cartwright <julia@ni.com>
To: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Carsten Emde <C.Emde@osadl.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
John Kacur <jkacur@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Daniel Wagner <daniel.wagner@siemens.com>,
tom.zanussi@linux.intel.com,
Peter Zijlstra <peterz@infradead.org>,
dvhart@infradead.org, stable@vger.kernel.org
Subject: [PATCH RT 01/22] futex: Fix pi_state->owner serialization
Date: Mon, 6 Aug 2018 04:17:17 -0500 [thread overview]
Message-ID: <43d23e5c64e32c64e18559ef810157700bf3eac4.1533540554.git.julia@ni.com> (raw)
In-Reply-To: <cover.1533540554.git.julia@ni.com>
From: Peter Zijlstra <peterz@infradead.org>
4.9.115-rt94-rc1 stable review patch.
If you have any objection to the inclusion of this patch, let me know.
--- 8< --- 8< --- 8< ---
[ 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 8ab0ddd4cf8f..47e42faad6c5 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -819,8 +819,6 @@ 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)
{
@@ -835,16 +833,22 @@ 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.
@@ -903,14 +907,15 @@ 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;
@@ -920,9 +925,10 @@ 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);
@@ -1204,6 +1210,10 @@ 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);
--
2.18.0
next prev parent reply other threads:[~2018-08-06 9:19 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-06 9:17 [PATCH RT 00/22] Linux 4.9.115-rt94-rc1 Julia Cartwright
2018-08-06 9:17 ` Julia Cartwright [this message]
2018-08-06 9:17 ` [PATCH RT 02/22] futex: Fix more put_pi_state() vs. exit_pi_state_list() races Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 03/22] futex: Avoid violating the 10th rule of futex Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 04/22] futex: Fix OWNER_DEAD fixup Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 05/22] rtmutex: Make rt_mutex_futex_unlock() safe for irq-off callsites Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 06/22] rcu: Do not include rtmutex_common.h unconditionally Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 07/22] rcu: Suppress lockdep false-positive ->boost_mtx complaints Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 08/22] sched, tracing: Fix trace_sched_pi_setprio() for deboosting Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 09/22] crypto: limit more FPU-enabled sections Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 10/22] arm*: disable NEON in kernel mode Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 11/22] mm/slub: close possible memory-leak in kmem_cache_alloc_bulk() Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 12/22] locking: add types.h Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 13/22] net: use task_struct instead of CPU number as the queue owner on -RT Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 14/22] Revert "rt,ntp: Move call to schedule_delayed_work() to helper thread" Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 15/22] Revert "block: blk-mq: Use swait" Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 16/22] block: blk-mq: move blk_queue_usage_counter_release() into process context Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 17/22] alarmtimer: Prevent live lock in alarm_cancel() Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 18/22] posix-timers: move the rcu head out of the union Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 19/22] locallock: provide {get,put}_locked_ptr() variants Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 20/22] squashfs: make use of local lock in multi_cpu decompressor Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 21/22] seqlock: provide the same ordering semantics as mainline Julia Cartwright
2018-08-06 9:17 ` [PATCH RT 22/22] Linux 4.9.115-rt94-rc1 Julia Cartwright
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