Re: 2.6.12-rc2-mm3

Andrew Morton
2005-04-14T00:24:03Z

Ed Tomlinson <tomlins@cam.org> wrote:
>
> > Don't think so - it works OK here. Checked the .config? Does the serial
> > port work if you do `echo foo > /dev/ttyS0'? ACPI?
>
> Turned out it was some old ups software that got reactivated on the box displaying the
> console - was a pain to disable it....

OK.

> In any case, when the box reboots there are not any messages. Any ideas on what debug
> options to enable or suggestions on how we can figure out the cause of the reboots.

There were a few problems in the task switching area - maybe that.

From: Ingo Molnar <mingo@elte.hu>

delay the reloading of segment registers into switch_mm(), so that if
the LDT size changes we dont get a (silent) fault and a zeroed selector
register upon reloading.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

25-akpm/arch/i386/kernel/process.c | 10 +++++-----
25-akpm/include/asm-i386/mmu_context.h | 7 +++++++
2 files changed, 12 insertions(+), 5 deletions(-)

diff -puN arch/i386/kernel/process.c~sched-unlocked-context-switches-fix arch/i386/kernel/process.c
--- 25/arch/i386/kernel/process.c~sched-unlocked-context-switches-fix 2005-04-12 03:43:07.254363568 -0700
+++ 25-akpm/arch/i386/kernel/process.c 2005-04-12 03:43:07.259362808 -0700
@@ -653,12 +653,12 @@ struct task_struct fastcall * __switch_t
asm volatile("mov %%gs,%0":"=m" (prev->gs));

/*
- * Restore %fs and %gs if needed.
+ * Clear selectors if needed:
*/
- if (unlikely(prev->fs | prev->gs | next->fs | next->gs)) {
- loadsegment(fs, next->fs);
- loadsegment(gs, next->gs);
- }
+ if (unlikely((prev->fs | prev->gs) && !(next->fs | next->gs))) {
+ loadsegment(fs, next->fs);
+ loadsegment(gs, next->gs);
+ }

/*
* Now maybe reload the debug registers
diff -puN include/asm-i386/mmu_context.h~sched-unlocked-context-switches-fix include/asm-i386/mmu_context.h
--- 25/include/asm-i386/mmu_context.h~sched-unlocked-context-switches-fix 2005-04-12 03:43:07.256363264 -0700
+++ 25-akpm/include/asm-i386/mmu_context.h 2005-04-12 03:43:07.260362656 -0700
@@ -61,6 +61,13 @@ static inline void switch_mm(struct mm_s
}
}
#endif
+ /*
+ * Now that we've switched the LDT, load segments:
+ */
+ if (unlikely(current->thread.fs | current->thread.gs)) {
+ loadsegment(fs, current->thread.fs);
+ loadsegment(gs, current->thread.gs);
+ }
}

#define deactivate_mm(tsk, mm) \
_