117 lines
4.5 KiB
Diff
117 lines
4.5 KiB
Diff
From d28abb43b0c0945556828845b30fb0b0f63eae02 Mon Sep 17 00:00:00 2001
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Message-Id: <d28abb43b0c0945556828845b30fb0b0f63eae02.1601675152.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Wed, 7 Mar 2012 20:51:03 +0100
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Subject: [PATCH 182/333] rt: Introduce cpu_chill()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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Retry loops on RT might loop forever when the modifying side was
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preempted. Add cpu_chill() to replace cpu_relax(). cpu_chill()
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defaults to cpu_relax() for non RT. On RT it puts the looping task to
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sleep for a tick so the preempted task can make progress.
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Steven Rostedt changed it to use a hrtimer instead of msleep():
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|Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken
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|up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is
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|called from softirq context, it may block the ksoftirqd() from running, in
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|which case, it may never wake up the msleep() causing the deadlock.
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+ bigeasy later changed to schedule_hrtimeout()
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|If a task calls cpu_chill() and gets woken up by a regular or spurious
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|wakeup and has a signal pending, then it exits the sleep loop in
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|do_nanosleep() and sets up the restart block. If restart->nanosleep.type is
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|not TI_NONE then this results in accessing a stale user pointer from a
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|previously interrupted syscall and a copy to user based on the stale
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|pointer or a BUG() when 'type' is not supported in nanosleep_copyout().
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+ bigeasy: add PF_NOFREEZE:
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| [....] Waiting for /dev to be fully populated...
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| =====================================
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| [ BUG: udevd/229 still has locks held! ]
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| 3.12.11-rt17 #23 Not tainted
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| -------------------------------------
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| 1 lock held by udevd/229:
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| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98
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| stack backtrace:
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| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23
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| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
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| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc)
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| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160)
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| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110)
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| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38)
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| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec)
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| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c)
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| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50)
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| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44)
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| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98)
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| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc)
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| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60)
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| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c)
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| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c)
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| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94)
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| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30)
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| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48)
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/delay.h | 6 ++++++
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kernel/time/hrtimer.c | 21 +++++++++++++++++++++
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2 files changed, 27 insertions(+)
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diff --git a/include/linux/delay.h b/include/linux/delay.h
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index b78bab4395d8..7c4bc414a504 100644
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--- a/include/linux/delay.h
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+++ b/include/linux/delay.h
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@@ -64,4 +64,10 @@ static inline void ssleep(unsigned int seconds)
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msleep(seconds * 1000);
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}
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+extern void cpu_chill(void);
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+#else
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+# define cpu_chill() cpu_relax()
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+#endif
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+
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#endif /* defined(_LINUX_DELAY_H) */
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diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
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index b800efb64238..98a771065818 100644
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--- a/kernel/time/hrtimer.c
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+++ b/kernel/time/hrtimer.c
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@@ -1897,6 +1897,27 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp,
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}
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#endif
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+/*
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+ * Sleep for 1 ms in hope whoever holds what we want will let it go.
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+ */
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+void cpu_chill(void)
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+{
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+ ktime_t chill_time;
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+ unsigned int freeze_flag = current->flags & PF_NOFREEZE;
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+
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+ chill_time = ktime_set(0, NSEC_PER_MSEC);
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+ set_current_state(TASK_UNINTERRUPTIBLE);
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+ current->flags |= PF_NOFREEZE;
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+ sleeping_lock_inc();
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+ schedule_hrtimeout(&chill_time, HRTIMER_MODE_REL_HARD);
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+ sleeping_lock_dec();
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+ if (!freeze_flag)
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+ current->flags &= ~PF_NOFREEZE;
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+}
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+EXPORT_SYMBOL(cpu_chill);
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+#endif
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+
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/*
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* Functions related to boot-time initialization:
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*/
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--
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2.17.1
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