Messages in this thread Patch in this message | | | Date | Mon, 13 Oct 2008 17:26:33 +0200 | From | Ingo Molnar <> | Subject | Re: [kerneloops] regression in 2.6.27 wrt "lock_page" and the "hwclock" program |
| |
* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> [ Ingo added to Cc just because this is obviously a x86 tree thing, and > tries to unify some trivial parts of the VM paths at the same time. ]
applied to tip/x86/urgent, thanks Linus!
do you agree with the changelog and can i add your Signed-off-by ?
Ingo
---------------------> From bdbe15671f9b3ad1264ed174f62563774f0abef9 Mon Sep 17 00:00:00 2001 From: Linus Torvalds <torvalds@linux-foundation.org> Date: Sun, 12 Oct 2008 13:16:12 -0700 Subject: [PATCH] x86/mm: do not trigger a kernel warning if user-space disables interrupts and generates a page fault
Arjan reported a spike in the following bug pattern in v2.6.27:
http://www.kerneloops.org/searchweek.php?search=lock_page
which happens because hwclock started triggering warnings due to a (correct) might_sleep() check in the MM code.
The warning occurs because hwclock uses this dubious sequence of code to run "atomic" code:
static unsigned long atomic(const char *name, unsigned long (*op)(unsigned long), unsigned long arg) { unsigned long v; __asm__ volatile ("cli"); v = (*op)(arg); __asm__ volatile ("sti"); return v; }
Then it pagefaults in that "atomic" section, triggering the warning.
There is no way the kernel could provide "atomicity" in this path, a page fault is a cannot-continue machine event so the kernel has to wait for the page to be filled in.
Even if it was just a minor fault we'd have to take locks and might have to spend quite a bit of time with interrupts disabled - not nice to irq latencies in general.
So instead just enable interrupts in the pagefault path unconditionally if we come from user-space, and handle the fault.
Also, while touching this code, unify some trivial parts of the x86 VM paths at the same time.
Reported-by: Arjan van de Ven <arjan@infradead.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> --- arch/x86/mm/fault.c | 30 +++++++++++------------------- 1 files changed, 11 insertions(+), 19 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index a742d75..ac2ad78 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -645,24 +645,23 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) } -#ifdef CONFIG_X86_32 - /* It's safe to allow irq's after cr2 has been saved and the vmalloc - fault has been handled. */ - if (regs->flags & (X86_EFLAGS_IF | X86_VM_MASK)) - local_irq_enable(); - /* - * If we're in an interrupt, have no user context or are running in an - * atomic region then we must not take the fault. + * It's safe to allow irq's after cr2 has been saved and the + * vmalloc fault has been handled. + * + * User-mode registers count as a user access even for any + * potential system fault or CPU buglet. */ - if (in_atomic() || !mm) - goto bad_area_nosemaphore; -#else /* CONFIG_X86_64 */ - if (likely(regs->flags & X86_EFLAGS_IF)) + if (user_mode_vm(regs)) { + local_irq_enable(); + error_code |= PF_USER; + } else if (regs->flags & X86_EFLAGS_IF) local_irq_enable(); +#ifdef CONFIG_X86_64 if (unlikely(error_code & PF_RSVD)) pgtable_bad(address, regs, error_code); +#endif /* * If we're in an interrupt, have no user context or are running in an @@ -671,14 +670,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) if (unlikely(in_atomic() || !mm)) goto bad_area_nosemaphore; - /* - * User-mode registers count as a user access even for any - * potential system fault or CPU buglet. - */ - if (user_mode_vm(regs)) - error_code |= PF_USER; again: -#endif /* When running in the kernel we expect faults to occur only to * addresses in user space. All other faults represent errors in the * kernel and should generate an OOPS. Unfortunately, in the case of an
| |