diff options
Diffstat (limited to 'features/rt/rt-Introduce-cpu_chill.patch')
| -rw-r--r-- | features/rt/rt-Introduce-cpu_chill.patch | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/features/rt/rt-Introduce-cpu_chill.patch b/features/rt/rt-Introduce-cpu_chill.patch new file mode 100644 index 00000000..2a837661 --- /dev/null +++ b/features/rt/rt-Introduce-cpu_chill.patch @@ -0,0 +1,121 @@ +From fccac47c4972dfaef50b0e080c60879a9d97bd25 Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Wed, 7 Mar 2012 20:51:03 +0100 +Subject: [PATCH 138/191] rt: Introduce cpu_chill() + +Retry loops on RT might loop forever when the modifying side was +preempted. Add cpu_chill() to replace cpu_relax(). cpu_chill() +defaults to cpu_relax() for non RT. On RT it puts the looping task to +sleep for a tick so the preempted task can make progress. + +Steven Rostedt changed it to use a hrtimer instead of msleep(): +| +|Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken +|up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is +|called from softirq context, it may block the ksoftirqd() from running, in +|which case, it may never wake up the msleep() causing the deadlock. + ++ bigeasy later changed to schedule_hrtimeout() +|If a task calls cpu_chill() and gets woken up by a regular or spurious +|wakeup and has a signal pending, then it exits the sleep loop in +|do_nanosleep() and sets up the restart block. If restart->nanosleep.type is +|not TI_NONE then this results in accessing a stale user pointer from a +|previously interrupted syscall and a copy to user based on the stale +|pointer or a BUG() when 'type' is not supported in nanosleep_copyout(). + ++ bigeasy: add PF_NOFREEZE: +| [....] Waiting for /dev to be fully populated... +| ===================================== +| [ BUG: udevd/229 still has locks held! ] +| 3.12.11-rt17 #23 Not tainted +| ------------------------------------- +| 1 lock held by udevd/229: +| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98 +| +| stack backtrace: +| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23 +| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14) +| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc) +| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160) +| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110) +| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38) +| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec) +| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c) +| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50) +| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44) +| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98) +| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc) +| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60) +| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c) +| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c) +| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94) +| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30) +| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48) + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Steven Rostedt <rostedt@goodmis.org> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + include/linux/hrtimer.h | 6 ++++++ + kernel/time/hrtimer.c | 30 ++++++++++++++++++++++++++++++ + 2 files changed, 36 insertions(+) + +diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h +index bb5e7b0a4274..e425a26a5ed8 100644 +--- a/include/linux/hrtimer.h ++++ b/include/linux/hrtimer.h +@@ -540,4 +540,10 @@ int hrtimers_dead_cpu(unsigned int cpu); + #define hrtimers_dead_cpu NULL + #endif + ++#ifdef CONFIG_PREEMPT_RT ++extern void cpu_chill(void); ++#else ++# define cpu_chill() cpu_relax() ++#endif ++ + #endif +diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c +index 788b9d137de4..3fa18a01f5b2 100644 +--- a/kernel/time/hrtimer.c ++++ b/kernel/time/hrtimer.c +@@ -2006,6 +2006,36 @@ SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __user *, rqtp, + } + #endif + ++#ifdef CONFIG_PREEMPT_RT ++/* ++ * Sleep for 1 ms in hope whoever holds what we want will let it go. ++ */ ++void cpu_chill(void) ++{ ++ unsigned int freeze_flag = current->flags & PF_NOFREEZE; ++ struct task_struct *self = current; ++ ktime_t chill_time; ++ ++ raw_spin_lock_irq(&self->pi_lock); ++ self->saved_state = self->state; ++ __set_current_state_no_track(TASK_UNINTERRUPTIBLE); ++ raw_spin_unlock_irq(&self->pi_lock); ++ ++ chill_time = ktime_set(0, NSEC_PER_MSEC); ++ ++ current->flags |= PF_NOFREEZE; ++ schedule_hrtimeout(&chill_time, HRTIMER_MODE_REL_HARD); ++ if (!freeze_flag) ++ current->flags &= ~PF_NOFREEZE; ++ ++ raw_spin_lock_irq(&self->pi_lock); ++ __set_current_state_no_track(self->saved_state); ++ self->saved_state = TASK_RUNNING; ++ raw_spin_unlock_irq(&self->pi_lock); ++} ++EXPORT_SYMBOL(cpu_chill); ++#endif ++ + /* + * Functions related to boot-time initialization: + */ +-- +2.19.1 + |