[ 3.8.y.z extended stable ] Patch "module: do percpu allocation after uniqueness check. No, really!" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    module: do percpu allocation after uniqueness check.  No, really!

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From be999474e80bd2a5bca6c4836dedd4ec0a131265 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty at rustcorp.com.au>
Date: Wed, 3 Jul 2013 10:06:28 +0930
Subject: module: do percpu allocation after uniqueness check.  No, really!

commit 8d8022e8aba85192e937f1f0f7450e256d66ae5c upstream.

v3.8-rc1-5-g1fb9341 was supposed to stop parallel kvm loads exhausting
percpu memory on large machines:

    Now we have a new state MODULE_STATE_UNFORMED, we can insert the
    module into the list (and thus guarantee its uniqueness) before we
    allocate the per-cpu region.

In my defence, it didn't actually say the patch did this.  Just that
we "can".

This patch actually *does* it.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Tested-by: Jim Hull <jim.hull at hp.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/module.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index eab0827..af2c7e6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2930,7 +2930,6 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 {
 	/* Module within temporary copy. */
 	struct module *mod;
-	Elf_Shdr *pcpusec;
 	int err;

 	mod = setup_load_info(info, flags);
@@ -2945,17 +2944,10 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 	err = module_frob_arch_sections(info->hdr, info->sechdrs,
 					info->secstrings, mod);
 	if (err < 0)
-		goto out;
+		return ERR_PTR(err);

-	pcpusec = &info->sechdrs[info->index.pcpu];
-	if (pcpusec->sh_size) {
-		/* We have a special allocation for this section. */
-		err = percpu_modalloc(mod,
-				      pcpusec->sh_size, pcpusec->sh_addralign);
-		if (err)
-			goto out;
-		pcpusec->sh_flags &= ~(unsigned long)SHF_ALLOC;
-	}
+	/* We will do a special allocation for per-cpu sections later. */
+	info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;

 	/* Determine total sizes, and put offsets in sh_entsize.  For now
 	   this is done generically; there doesn't appear to be any
@@ -2966,17 +2958,22 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 	/* Allocate and move to the final place */
 	err = move_module(mod, info);
 	if (err)
-		goto free_percpu;
+		return ERR_PTR(err);

 	/* Module has been copied to its final place now: return it. */
 	mod = (void *)info->sechdrs[info->index.mod].sh_addr;
 	kmemleak_load_module(mod, info);
 	return mod;
+}

-free_percpu:
-	percpu_modfree(mod);
-out:
-	return ERR_PTR(err);
+static int alloc_module_percpu(struct module *mod, struct load_info *info)
+{
+	Elf_Shdr *pcpusec = &info->sechdrs[info->index.pcpu];
+	if (!pcpusec->sh_size)
+		return 0;
+
+	/* We have a special allocation for this section. */
+	return percpu_modalloc(mod, pcpusec->sh_size, pcpusec->sh_addralign);
 }

 /* mod is no longer valid after this! */
@@ -3196,6 +3193,11 @@ again:
 		add_taint_module(mod, TAINT_FORCED_MODULE);
 #endif

+	/* To avoid stressing percpu allocator, do this once we're unique. */
+	err = alloc_module_percpu(mod, info);
+	if (err)
+		goto unlink_mod;
+
 	/* Now module is in final location, initialize linked lists, etc. */
 	err = module_unload_init(mod);
 	if (err)
--
1.8.1.2