diff options
Diffstat (limited to 'debian/patches-rt/futex-workaround-migrate_disable-enable-in-different.patch')
| -rw-r--r-- | debian/patches-rt/futex-workaround-migrate_disable-enable-in-different.patch | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/debian/patches-rt/futex-workaround-migrate_disable-enable-in-different.patch b/debian/patches-rt/futex-workaround-migrate_disable-enable-in-different.patch new file mode 100644 index 000000000..7d89fbcbf --- /dev/null +++ b/debian/patches-rt/futex-workaround-migrate_disable-enable-in-different.patch @@ -0,0 +1,67 @@ +From: Thomas Gleixner <tglx@linutronix.de> +Date: Wed, 8 Mar 2017 14:23:35 +0100 +Subject: [PATCH] futex: workaround migrate_disable/enable in different context +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz + +migrate_enable() invokes __schedule() and it expects a preempt count of one. +Holding a raw_spinlock_t with disabled interrupts should not allow scheduling. + +These little hacks ensure that we don't schedule while we lock the hb lockwith +interrupts enabled and unlock it with interrupts disabled. + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +[XXX: As per PeterZ suggesstion + set_thread_flag(TIF_NEED_RESCHED); preempt_fold_need_resched() + would trigger a scheduler invocation on the last preempt_enable() which in + turn would allow to drop this. +] +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/futex.c | 18 ++++++++++++++++++ + 1 file changed, 18 insertions(+) + +--- a/kernel/futex.c ++++ b/kernel/futex.c +@@ -2980,6 +2980,14 @@ static int futex_lock_pi(u32 __user *uad + * before __rt_mutex_start_proxy_lock() is done. + */ + raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); ++ /* ++ * the migrate_disable() here disables migration in the in_atomic() fast ++ * path which is enabled again in the following spin_unlock(). We have ++ * one migrate_disable() pending in the slow-path which is reversed ++ * after the raw_spin_unlock_irq() where we leave the atomic context. ++ */ ++ migrate_disable(); ++ + spin_unlock(q.lock_ptr); + /* + * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter +@@ -2988,6 +2996,7 @@ static int futex_lock_pi(u32 __user *uad + */ + 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(); + + if (ret) { + if (ret == 1) +@@ -3136,10 +3145,19 @@ static int futex_unlock_pi(u32 __user *u + * rt_waiter. Also see the WARN in wake_futex_pi(). + */ + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); ++ /* ++ * Magic trickery for now to make the RT migrate disable ++ * logic happy. The following spin_unlock() happens with ++ * interrupts disabled so the internal migrate_enable() ++ * won't undo the migrate_disable() which was issued when ++ * locking hb->lock. ++ */ ++ migrate_disable(); + spin_unlock(&hb->lock); + + /* drops pi_state->pi_mutex.wait_lock */ + ret = wake_futex_pi(uaddr, uval, pi_state); ++ migrate_enable(); + + put_pi_state(pi_state); + |