Patchwork [RFC/PATCH] mm: Pass virtual address to [__]p{te,ud,md}_free_tlb()

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Submitter Benjamin Herrenschmidt
Date July 28, 2009, 12:17 a.m.
Message ID <1248740260.30993.26.camel@pasglop>
Download mbox | patch
Permalink /patch/30283/
State Accepted
Headers show

Comments

Benjamin Herrenschmidt - July 28, 2009, 12:17 a.m.
On Mon, 2009-07-27 at 12:11 -0700, Linus Torvalds wrote:
> 
> On Thu, 23 Jul 2009, Benjamin Herrenschmidt wrote:
> > 
> > Hrm... my powerpc-next branch will contain stuff that depend on it, so
> > I'll probably have to pull it in though, unless I tell all my
> > sub-maintainers to also pull from that other branch first :-)
> 
> Ok, I'll just apply the patch. It does look obvious enough.

There seem to be a MIPS and SH breakage as a result but I can't see
how my patch would have broken it, ie, it looks like the bug was
already in those two archs. The error is that it complains about a
duplicate definition of __pmd_free_tlb() between those arch pgalloc.h
and pgtable-nopmd.h

For MIPS, when CONFIG_32BIT is set, asm/pgalloc.h redefines
__pmd_free_tlb despite the fact that it's already defined by
asm-generic/pgtable-nopmd.h (via via pgtable.h via linux/mm.h).

I -suspect- what happens is that the compiler, before, would ignore the
double definition (or maybe just warn) due to the definition being
strictly identical. With the new argument added, it's no longer the case
as it's called "a" in asm-generic and "addr" in mips... oops.

In any case, can Ralf and Paul check if the following patch is correct ?

>From 41928c7945d855ae0eb053eadad590ab6876847e Mon Sep 17 00:00:00 2001
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Tue, 28 Jul 2009 10:16:48 +1000
Subject: [PATCH] mm: Remove duplicate definitions in MIPS and SH

Those definitions are already provided by asm-generic

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 arch/mips/include/asm/pgalloc.h |   11 -----------
 arch/sh/include/asm/pgalloc.h   |    8 --------
 2 files changed, 0 insertions(+), 19 deletions(-)
Paul Mundt - July 28, 2009, 12:25 a.m.
On Tue, Jul 28, 2009 at 10:17:40AM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2009-07-27 at 12:11 -0700, Linus Torvalds wrote:
> > On Thu, 23 Jul 2009, Benjamin Herrenschmidt wrote:
> > > 
> > > Hrm... my powerpc-next branch will contain stuff that depend on it, so
> > > I'll probably have to pull it in though, unless I tell all my
> > > sub-maintainers to also pull from that other branch first :-)
> > 
> > Ok, I'll just apply the patch. It does look obvious enough.
> 
> There seem to be a MIPS and SH breakage as a result but I can't see
> how my patch would have broken it, ie, it looks like the bug was
> already in those two archs. The error is that it complains about a
> duplicate definition of __pmd_free_tlb() between those arch pgalloc.h
> and pgtable-nopmd.h
> 
> For MIPS, when CONFIG_32BIT is set, asm/pgalloc.h redefines
> __pmd_free_tlb despite the fact that it's already defined by
> asm-generic/pgtable-nopmd.h (via via pgtable.h via linux/mm.h).
> 
> I -suspect- what happens is that the compiler, before, would ignore the
> double definition (or maybe just warn) due to the definition being
> strictly identical. With the new argument added, it's no longer the case
> as it's called "a" in asm-generic and "addr" in mips... oops.
> 
> In any case, can Ralf and Paul check if the following patch is correct ?
> 
Yup, that seems to be what happened. I've never seen a warning about this
with any compiler version, otherwise we would have caught this much
earlier. As soon as the addr -> a rename took place it blew up
immediately as a redefinition. Is there a magical gcc flag we can turn on
to warn on identical definitions, even if just for testing?

> >From 41928c7945d855ae0eb053eadad590ab6876847e Mon Sep 17 00:00:00 2001
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Date: Tue, 28 Jul 2009 10:16:48 +1000
> Subject: [PATCH] mm: Remove duplicate definitions in MIPS and SH
> 
> Those definitions are already provided by asm-generic
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Builds and boots fine, thanks.

Acked-by: Paul Mundt <lethal@linux-sh.org>
Linus Torvalds - July 28, 2009, 12:41 a.m.
On Tue, 28 Jul 2009, Paul Mundt wrote:
>
> Yup, that seems to be what happened. I've never seen a warning about this
> with any compiler version, otherwise we would have caught this much
> earlier. As soon as the addr -> a rename took place it blew up
> immediately as a redefinition. Is there a magical gcc flag we can turn on
> to warn on identical definitions, even if just for testing?

No, this is actually defined C behavior - identical macro redefinitions 
are ok. That's very much on purpose, and allows different header files to 
use an identical #define to define some common macro.

Strictly speaking, this is a "safety feature", in that you obviously 
_could_ just always do a #undef+#define, but such a case would be able to 
redefine a macro even if the new definition didn't match the old one. So 
the C pre-processor rules is that you can safely re-define something if 
you re-define it identically.

Of course, we could make the rules for the kernel be stricter, but I don't 
know if there are any flags to warn about it, since it's such a standard C 
feature: the lack of warning is _not_ an accident.

It would be trivial to teach sparse to warn about it, of course. Look at 
sparse/pre-process.c, function do_handle_define(). Notice how it literally 
checks that any previous #define is identical in both expansion and 
argument list, with:

		if (token_list_different(sym->expansion, expansion) ||
		    token_list_different(sym->arglist, arglist)) {

and just make token_list_different() always return true (this is the only 
use of that function).

I haven't checked if such a change would actually result in a lot of 
warnings.

		Linus

Patch

diff --git a/arch/mips/include/asm/pgalloc.h b/arch/mips/include/asm/pgalloc.h
index f705735..3738f4b 100644
--- a/arch/mips/include/asm/pgalloc.h
+++ b/arch/mips/include/asm/pgalloc.h
@@ -104,17 +104,6 @@  do {							\
 	tlb_remove_page((tlb), pte);			\
 } while (0)
 
-#ifdef CONFIG_32BIT
-
-/*
- * allocating and freeing a pmd is trivial: the 1-entry pmd is
- * inside the pgd, so has no extra memory associated with it.
- */
-#define pmd_free(mm, x)			do { } while (0)
-#define __pmd_free_tlb(tlb, x, addr)	do { } while (0)
-
-#endif
-
 #ifdef CONFIG_64BIT
 
 static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
diff --git a/arch/sh/include/asm/pgalloc.h b/arch/sh/include/asm/pgalloc.h
index 89a4827..63ca37b 100644
--- a/arch/sh/include/asm/pgalloc.h
+++ b/arch/sh/include/asm/pgalloc.h
@@ -79,14 +79,6 @@  do {							\
 	tlb_remove_page((tlb), (pte));			\
 } while (0)
 
-/*
- * allocating and freeing a pmd is trivial: the 1-entry pmd is
- * inside the pgd, so has no extra memory associated with it.
- */
-
-#define pmd_free(mm, x)			do { } while (0)
-#define __pmd_free_tlb(tlb,x,addr)	do { } while (0)
-
 static inline void check_pgt_cache(void)
 {
 	quicklist_trim(QUICK_PGD, NULL, 25, 16);