[PATCH RT 0/3] Linux v4.9.268-rt180-rc1

[PATCH RT 0/3] Linux v4.9.268-rt180-rc1

[Luis Claudio R. Goncalves]

Dear RT Folks,

This is the RT stable review cycle of patch 4.9.268-rt180-rc1.

Please scream at me if I messed something up. Please test the patches
too.

The -rc release will be uploaded to kernel.org and will be deleted
when the final release is out. This is just a review release (or
release candidate).

The pre-releases will not be pushed to the git repository, only the
final release is.

If all goes well, this patch will be converted to the next main
release on 2021-06-07.

To build 4.9.268-rt180-rc1 directly, the following patches should be applied:

  https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.9.tar.xz

  https://www.kernel.org/pub/linux/kernel/v4.x/patch-4.9.268.xz

  https://www.kernel.org/pub/linux/kernel/projects/rt/4.9/patch-4.9.268-rt180-rc1.patch.xz


You can also build from 4.9.268-rt179 by applying the incremental patch:

  https://www.kernel.org/pub/linux/kernel/projects/rt/4.9/incr/patch-4.9.268-rt179-rt180-rc1.patch.xz

Enjoy,

-- Luis


Ben Hutchings (1):
  futex: Fix mis-merge of 4.9-stable changes with 4.9-rt

Luis Claudio R. Goncalves (1):
  Linux 4.9.268-rt180-rc1

Oleg Nesterov (1):
  ptrace: fix ptrace_unfreeze_traced() race with rt-lock

 kernel/futex.c                  | 39 ++++++++++++---------------------
 kernel/locking/rtmutex.c        |  3 +--
 kernel/locking/rtmutex_common.h |  1 -
 kernel/ptrace.c                 | 23 ++++++++++++-------
 localversion-rt                 |  2 +-
 5 files changed, 31 insertions(+), 37 deletions(-)

-- 
2.31.1

[PATCH RT 1/3] futex: Fix mis-merge of 4.9-stable changes with 4.9-rt

[Luis Claudio R. Goncalves]

From: Ben Hutchings <ben@decadent.org.uk>

v4.9.268-rt180-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


The recent merges of futex changes from 4.9-stable into the 4.9-rt
tree effectively reverted:

* The deletion of calls to rt_mutex_futex_unlock() from futex_lock_pi()
  and futex_wait_requeue_pi() by commit b960d9ae7f76 "futex: Handle
  faults correctly for PI futexes".

* The deletion of uninitialized_var() by commit 48ab8e8e4059 "futex:
  Simplify fixup_pi_state_owner()".

* Commit c59b46c53fa1 "rtmutex: Handle non enqueued waiters gracefully".

Restore those changes.

Also resolve some other cosmetic differences from the 4.9-stable
version of futex.c and rtmutex_common.h due to slightly different
backports.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
 kernel/futex.c                  | 39 ++++++++++++---------------------
 kernel/locking/rtmutex.c        |  3 +--
 kernel/locking/rtmutex_common.h |  1 -
 3 files changed, 15 insertions(+), 28 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 93f2fb5b21b2d..7679831ed8094 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2465,9 +2465,9 @@ static void unqueue_me_pi(struct futex_q *q)
 static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
 				  struct task_struct *argowner)
 {
-	u32 uval, uninitialized_var(curval), newval, newtid;
 	struct futex_pi_state *pi_state = q->pi_state;
 	struct task_struct *oldowner, *newowner;
+	u32 uval, curval, newval, newtid;
 	int err = 0;
 
 	oldowner = pi_state->owner;
@@ -3005,9 +3005,10 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	 * and BUG when futex_unlock_pi() interleaves with this.
 	 *
 	 * Therefore acquire wait_lock while holding hb->lock, but drop the
-	 * latter before calling rt_mutex_start_proxy_lock(). This still fully
-	 * serializes against futex_unlock_pi() as that does the exact same
-	 * lock handoff sequence.
+	 * latter before calling __rt_mutex_start_proxy_lock(). This
+	 * interleaves with futex_unlock_pi() -- which does a similar lock
+	 * handoff -- such that the latter can observe the futex_q::pi_state
+	 * before __rt_mutex_start_proxy_lock() is done.
 	 */
 	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
 	/*
@@ -3019,6 +3020,11 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	migrate_disable();
 
 	spin_unlock(q.lock_ptr);
+	/*
+	 * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+	 * such that futex_unlock_pi() is guaranteed to observe the waiter when
+	 * it sees the futex_q::pi_state.
+	 */
 	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
 	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
 	migrate_enable();
@@ -3037,10 +3043,10 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 cleanup:
 	spin_lock(q.lock_ptr);
 	/*
-	 * If we failed to acquire the lock (signal/timeout), we must
+	 * If we failed to acquire the lock (deadlock/signal/timeout), we must
 	 * first acquire the hb->lock before removing the lock from the
-	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
-	 * wait lists consistent.
+	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
+	 * lists consistent.
 	 *
 	 * In particular; it is important that futex_unlock_pi() can not
 	 * observe this inconsistency.
@@ -3061,13 +3067,6 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	if (res)
 		ret = (res < 0) ? res : 0;
 
-	/*
-	 * If fixup_owner() faulted and was unable to handle the fault, unlock
-	 * it and return the fault to userspace.
-	 */
-	if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
-		rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
-
 	/* Unqueue and drop the lock */
 	unqueue_me_pi(&q);
 
@@ -3170,7 +3169,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 		migrate_disable();
 		spin_unlock(&hb->lock);
 
-		/* Drops pi_state->pi_mutex.wait_lock */
+		/* drops pi_state->pi_mutex.wait_lock */
 		ret = wake_futex_pi(uaddr, uval, pi_state);
 
 		migrate_enable();
@@ -3460,8 +3459,6 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 			spin_lock(&hb2->lock);
 			BUG_ON(&hb2->lock != q.lock_ptr);
 			ret = fixup_pi_state_owner(uaddr2, &q, current);
-			if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current)
-				rt_mutex_futex_unlock(&q.pi_state->pi_mutex);
 			/*
 			 * Drop the reference to the pi state which
 			 * the requeue_pi() code acquired for us.
@@ -3504,14 +3501,6 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 		if (res)
 			ret = (res < 0) ? res : 0;
 
-		/*
-		 * If fixup_pi_state_owner() faulted and was unable to handle
-		 * the fault, unlock the rt_mutex and return the fault to
-		 * userspace.
-		 */
-		if (ret && rt_mutex_owner(pi_mutex) == current)
-			rt_mutex_futex_unlock(pi_mutex);
-
 		/* Unqueue and drop the lock. */
 		unqueue_me_pi(&q);
 	}
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 9816892558b82..a7f971a601919 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2397,7 +2397,7 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 
 	raw_spin_lock_irq(&lock->wait_lock);
 	ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
-	if (unlikely(ret))
+	if (ret && rt_mutex_has_waiters(lock))
 		remove_waiter(lock, waiter);
 	raw_spin_unlock_irq(&lock->wait_lock);
 
@@ -2526,7 +2526,6 @@ bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
 		remove_waiter(lock, waiter);
 		cleanup = true;
 	}
-
 	/*
 	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 	 * have to fix that up.
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 750bad6849e21..98debc11953fb 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -119,7 +119,6 @@ extern int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
 			       struct rt_mutex_waiter *waiter);
 extern bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
 				 struct rt_mutex_waiter *waiter);
-
 extern int rt_mutex_futex_trylock(struct rt_mutex *l);
 extern int __rt_mutex_futex_trylock(struct rt_mutex *l);
 
-- 
2.31.1

[PATCH RT 2/3] ptrace: fix ptrace_unfreeze_traced() race with rt-lock

[Luis Claudio R. Goncalves]

From: Oleg Nesterov <oleg@redhat.com>

v4.9.268-rt180-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit 0fdc91971b34cf6857b4cfd8c322ae936cfc189b ]

The patch "ptrace: fix ptrace vs tasklist_lock race" changed
ptrace_freeze_traced() to take task->saved_state into account, but
ptrace_unfreeze_traced() has the same problem and needs a similar fix:
it should check/update both ->state and ->saved_state.

Reported-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Fixes: "ptrace: fix ptrace vs tasklist_lock race"
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
 kernel/ptrace.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 7245160f37801..809840af4ab60 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -187,8 +187,8 @@ static bool ptrace_freeze_traced(struct task_struct *task)
 
 static void ptrace_unfreeze_traced(struct task_struct *task)
 {
-	if (task->state != __TASK_TRACED)
-		return;
+	unsigned long flags;
+	bool frozen = true;
 
 	WARN_ON(!task->ptrace || task->parent != current);
 
@@ -197,12 +197,19 @@ static void ptrace_unfreeze_traced(struct task_struct *task)
 	 * Recheck state under the lock to close this race.
 	 */
 	spin_lock_irq(&task->sighand->siglock);
-	if (task->state == __TASK_TRACED) {
-		if (__fatal_signal_pending(task))
-			wake_up_state(task, __TASK_TRACED);
-		else
-			task->state = TASK_TRACED;
-	}
+
+	raw_spin_lock_irqsave(&task->pi_lock, flags);
+	if (task->state == __TASK_TRACED)
+		task->state = TASK_TRACED;
+	else if (task->saved_state == __TASK_TRACED)
+		task->saved_state = TASK_TRACED;
+	else
+		frozen = false;
+	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+	if (frozen && __fatal_signal_pending(task))
+		wake_up_state(task, __TASK_TRACED);
+
 	spin_unlock_irq(&task->sighand->siglock);
 }
 
-- 
2.31.1

[PATCH RT 3/3] Linux 4.9.268-rt180-rc1

[Luis Claudio R. Goncalves]

v4.9.268-rt180-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
 localversion-rt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/localversion-rt b/localversion-rt
index 326e314b799eb..df629541e5443 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt179
+-rt180-rc1
-- 
2.31.1