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Date: Fri, 12 Jun 2009 14:34:00 +0300
From: Pekka Enberg <penberg@...helsinki.fi>
To: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, npiggin@...e.de,
akpm@...ux-foundation.org, cl@...ux-foundation.org,
torvalds@...ux-foundation.org
Subject: Re: [PATCH v2] slab,slub: ignore __GFP_WAIT if we're booting or
suspending
Hi Ben,
On Fri, 2009-06-12 at 21:11 +1000, Benjamin Herrenschmidt wrote:
> > OK, but that means we need to fix up every single caller. I'm fine
> > with that but Ben is not. As I am unable to test powerpc here, I am
> > inclined to just merge Ben's patch as "obviously correct".
> >
> > That does not mean we can't introduce GFP_BOOT later on if we want to. Hmm?
>
> Again, you are missing part of the picture. Yes we -can- fix all the
> -direct- callers that are obviously only be run at boot time. But what
> about all the indirect ones (or even direct ones) that can be called
> either at boot time or later. vmalloc() is the perfect example (or more
> precisely __get_vm_area() which brings in ioremap etc...) but there are
> many more.
No, I don't think I am. We can fix up the indirect callers too by making
sure we pass the proper GFP flag and propagate that all the way down.
Yes, this is potentially quite a bit of code churn which is why I do see
your patch being the easy way out.
That said, Nick and Ingo seem to think special-casing is questionable
and I haven't had green light for any of the patches yet. The gfp
sanitization patch adds some overhead to kmalloc() and page allocator
paths which is obviously a concern.
So while we continue to discuss this, I'd really like to proceed with
the patch below. At least it should allow people to boot their kernels
(although it will produce warnings). I really don't want to keep other
people waiting for us to reach a resolution on this. Are you OK with
that?
Pekka
>>From f6b726dae91cc74fb3a00f192932ec4fe0949875 Mon Sep 17 00:00:00 2001
From: Pekka Enberg <penberg@...helsinki.fi>
Date: Fri, 12 Jun 2009 14:03:06 +0300
Subject: [PATCH] slab: don't enable interrupts during early boot
As explained by Benjamin Herrenschmidt:
Oh and btw, your patch alone doesn't fix powerpc, because it's missing
a whole bunch of GFP_KERNEL's in the arch code... You would have to
grep the entire kernel for things that check slab_is_available() and
even then you'll be missing some.
For example, slab_is_available() didn't always exist, and so in the
early days on powerpc, we used a mem_init_done global that is set form
mem_init() (not perfect but works in practice). And we still have code
using that to do the test.
Therefore, mask out __GFP_WAIT in the slab allocators in early boot code to
avoid enabling interrupts.
Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
---
include/linux/slab.h | 2 ++
include/linux/slob_def.h | 5 +++++
include/linux/slub_def.h | 2 ++
init/main.c | 1 +
mm/slab.c | 22 ++++++++++++++++++++++
mm/slub.c | 18 ++++++++++++++++++
6 files changed, 50 insertions(+), 0 deletions(-)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 4880306..219b8fb 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -319,4 +319,6 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)
return kmalloc_node(size, flags | __GFP_ZERO, node);
}
+void __init kmem_cache_init_late(void);
+
#endif /* _LINUX_SLAB_H */
diff --git a/include/linux/slob_def.h b/include/linux/slob_def.h
index 0ec00b3..bb5368d 100644
--- a/include/linux/slob_def.h
+++ b/include/linux/slob_def.h
@@ -34,4 +34,9 @@ static __always_inline void *__kmalloc(size_t size, gfp_t flags)
return kmalloc(size, flags);
}
+static inline void kmem_cache_init_late(void)
+{
+ /* Nothing to do */
+}
+
#endif /* __LINUX_SLOB_DEF_H */
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index be5d40c..4dcbc2c 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -302,4 +302,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
}
#endif
+void __init kmem_cache_init_late(void);
+
#endif /* _LINUX_SLUB_DEF_H */
diff --git a/init/main.c b/init/main.c
index b3e8f14..f6204f7 100644
--- a/init/main.c
+++ b/init/main.c
@@ -640,6 +640,7 @@ asmlinkage void __init start_kernel(void)
"enabled early\n");
early_boot_irqs_on();
local_irq_enable();
+ kmem_cache_init_late();
/*
* HACK ALERT! This is early. We're enabling the console before
diff --git a/mm/slab.c b/mm/slab.c
index f46b65d..a785808 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -304,6 +304,12 @@ struct kmem_list3 {
};
/*
+ * The slab allocator is initialized with interrupts disabled. Therefore, make
+ * sure early boot allocations don't accidentally enable interrupts.
+ */
+static gfp_t slab_gfp_mask __read_mostly = __GFP_BITS_MASK & ~__GFP_WAIT;
+
+/*
* Need this for bootstrapping a per node allocator.
*/
#define NUM_INIT_LISTS (3 * MAX_NUMNODES)
@@ -1654,6 +1660,14 @@ void __init kmem_cache_init(void)
*/
}
+void __init kmem_cache_init_late(void)
+{
+ /*
+ * Interrupts are enabled now so all GFP allocations are safe.
+ */
+ slab_gfp_mask = __GFP_BITS_MASK;
+}
+
static int __init cpucache_init(void)
{
int cpu;
@@ -2812,6 +2826,10 @@ static int cache_grow(struct kmem_cache *cachep,
offset *= cachep->colour_off;
+ /* Lets avoid crashing in early boot code. */
+ if (WARN_ON_ONCE((local_flags & ~slab_gfp_mask) != 0))
+ local_flags &= slab_gfp_mask;
+
if (local_flags & __GFP_WAIT)
local_irq_enable();
@@ -3237,6 +3255,10 @@ retry:
}
if (!obj) {
+ /* Lets avoid crashing in early boot code. */
+ if (WARN_ON_ONCE((local_flags & ~slab_gfp_mask) != 0))
+ local_flags &= slab_gfp_mask;
+
/*
* This allocation will be performed within the constraints
* of the current cpuset / memory policy requirements.
diff --git a/mm/slub.c b/mm/slub.c
index 3964d3c..651bb34 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -178,6 +178,12 @@ static enum {
SYSFS /* Sysfs up */
} slab_state = DOWN;
+/*
+ * The slab allocator is initialized with interrupts disabled. Therefore, make
+ * sure early boot allocations don't accidentally enable interrupts.
+ */
+static gfp_t slab_gfp_mask __read_mostly = __GFP_BITS_MASK & ~__GFP_WAIT;
+
/* A list of all slab caches on the system */
static DECLARE_RWSEM(slub_lock);
static LIST_HEAD(slab_caches);
@@ -1548,6 +1554,10 @@ new_slab:
goto load_freelist;
}
+ /* Lets avoid crashing in early boot code. */
+ if (WARN_ON_ONCE((gfpflags & ~slab_gfp_mask) != 0))
+ gfpflags &= slab_gfp_mask;
+
if (gfpflags & __GFP_WAIT)
local_irq_enable();
@@ -3104,6 +3114,14 @@ void __init kmem_cache_init(void)
nr_cpu_ids, nr_node_ids);
}
+void __init kmem_cache_init_late(void)
+{
+ /*
+ * Interrupts are enabled now so all GFP allocations are safe.
+ */
+ slab_gfp_mask = __GFP_BITS_MASK;
+}
+
/*
* Find a mergeable slab cache
*/
--
1.6.0.4
--
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