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Commit acb04058 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/clock: Fix hotplug crash 



Mike reported that he could trigger the WARN_ON_ONCE() in
set_sched_clock_stable() using hotplug.

This exposed a fundamental problem with the interface, we should never
mark the TSC stable if we ever find it to be unstable. Therefore
set_sched_clock_stable() is a broken interface.

The reason it existed is that not having it is a pain, it means all
relevant architecture code needs to call clear_sched_clock_stable()
where appropriate.

Of the three architectures that select HAVE_UNSTABLE_SCHED_CLOCK ia64
and parisc are trivial in that they never called
set_sched_clock_stable(), so add an unconditional call to
clear_sched_clock_stable() to them.

For x86 the story is a lot more involved, and what this patch tries to
do is ensure we preserve the status quo. So even is Cyrix or Transmeta
have usable TSC they never called set_sched_clock_stable() so they now
get an explicit mark unstable.

Reported-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9881b024 ("sched/clock: Delay switching sched_clock to stable")
Link: http://lkml.kernel.org/r/20170119133633.GB6536@twins.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 02cfdc95

arch/ia64/kernel/setup.c

+2 −0
Original line number Diff line number Diff line
@@ -619,6 +619,8 @@ setup_arch (char **cmdline_p) 
	check_sal_cache_flush();

#endif

	paging_init();



	clear_sched_clock_stable();

}



/*

arch/parisc/kernel/setup.c

+2 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ 
#undef PCI_DEBUG

#include <linux/proc_fs.h>

#include <linux/export.h>

#include <linux/sched.h>



#include <asm/processor.h>

#include <asm/sections.h>
@@ -176,6 +177,7 @@ void __init setup_arch(char **cmdline_p) 
	conswitchp = &dummy_con;	/* we use do_take_over_console() later ! */

#endif



	clear_sched_clock_stable();

}



/*

arch/x86/kernel/cpu/amd.c

+4 −2
Original line number Diff line number Diff line
@@ -548,8 +548,10 @@ static void early_init_amd(struct cpuinfo_x86 *c) 
	if (c->x86_power & (1 << 8)) {

		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);

		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);

		if (!check_tsc_unstable())

			set_sched_clock_stable();

		if (check_tsc_unstable())

			clear_sched_clock_stable();

	} else {

		clear_sched_clock_stable();

	}



	/* Bit 12 of 8000_0007 edx is accumulated power mechanism. */

arch/x86/kernel/cpu/centaur.c

+4 −2
Original line number Diff line number Diff line 
#include <linux/bitops.h>

#include <linux/kernel.h>



#include <linux/sched.h>



#include <asm/cpufeature.h>

#include <asm/e820.h>
@@ -104,6 +104,8 @@ static void early_init_centaur(struct cpuinfo_x86 *c) 
#ifdef CONFIG_X86_64

	set_cpu_cap(c, X86_FEATURE_SYSENTER32);

#endif



	clear_sched_clock_stable();

}



static void init_centaur(struct cpuinfo_x86 *c)

arch/x86/kernel/cpu/common.c

+3 −0
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ static void default_init(struct cpuinfo_x86 *c) 
			strcpy(c->x86_model_id, "386");

	}

#endif

	clear_sched_clock_stable();

}



static const struct cpu_dev default_cpu = {
@@ -1055,6 +1056,8 @@ static void identify_cpu(struct cpuinfo_x86 *c) 
	 */

	if (this_cpu->c_init)

		this_cpu->c_init(c);

	else

		clear_sched_clock_stable();



	/* Disable the PN if appropriate */

	squash_the_stupid_serial_number(c);