Re: [RFC][PATCH] PM: disable nonboot cpus before suspending devices

[Rafael J. Wysocki]

On Thursday 04 February 2010, Andrew Morton wrote:
> On Wed, 3 Feb 2010 23:34:37 +0100
> "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> 
> > On Wednesday 03 February 2010, Andrew Morton wrote:
> > > On Wed, 3 Feb 2010 02:44:23 +0100 "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> > > 
> > > > +static inline gfp_t clear_gfp_allowed_mask(gfp_t mask)
> > > > +{
> > > > +	gfp_t ret = gfp_allowed_mask;
> > > > +	gfp_allowed_mask &= ~mask;
> > > > +	return ret;
> > > > +}
> > > 
> > > Fair enuf.
> > > 
> > > Of course, this is all horridly racy/buggy without locking.  Would I be
> > > correct in hoping that all the callers happen when the system is in
> > > everyone-is-frozen mode?
> > 
> > As far as I can tell, gfp_allowed_mask is only touched during init apart from
> > this.
> 
> Well yes - the new interfaces are the problem - they're racy!
> 
> > > Perhaps we should add some documentation (or even an assertion) to
> > > prevent someone from using these interfaces from within normal code.
> > 
> > I thought about that, but didn't invent anything smart enough.
> > 
> > Well, maybe except for a comment like "this must be called with pm_mutex held",
> > because that's the only case when it would be really safe.
> 
> Is that the locking rule?  My above guess was incorrect?
> 
> Maybe slip a
> 
> 	BUG_ON(!mutex_is_locked(&pm_mutex));
> 
> in there?

That actually is a good idea, although I prefer WARN_ON (BUG_ON would be
rather blunt, so to speak, as it could kill setups not using suspend/hibernate
at all).

Updated patch follows.

Rafael

---
From: Rafael J. Wysocki <rjw@xxxxxxx>
Subject: MM / PM: Force GFP_NOIO during suspend/hibernation and resume (rev. 3)

There are quite a few GFP_KERNEL memory allocations made during
suspend/hibernation and resume that may cause the system to hang,
because the I/O operations they depend on cannot be completed due to
the underlying devices being suspended.

Mitigate this problem by clearing the __GFP_IO and __GFP_FS bits in
gfp_allowed_mask before suspend/hibernation and restoring the
original values of these bits in gfp_allowed_mask durig the
subsequent resume.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Reported-by: Maxim Levitsky <maximlevitsky@xxxxxxxxx>
---
 include/linux/gfp.h      |    7 +++----
 init/main.c              |    2 +-
 kernel/power/hibernate.c |    9 +++++++++
 kernel/power/suspend.c   |    3 +++
 mm/page_alloc.c          |   24 ++++++++++++++++++++++++
 5 files changed, 40 insertions(+), 5 deletions(-)

Index: linux-2.6/include/linux/gfp.h
===================================================================
--- linux-2.6.orig/include/linux/gfp.h
+++ linux-2.6/include/linux/gfp.h
@@ -83,6 +83,7 @@ struct vm_area_struct;
 #define GFP_HIGHUSER_MOVABLE	(__GFP_WAIT | __GFP_IO | __GFP_FS | \
 				 __GFP_HARDWALL | __GFP_HIGHMEM | \
 				 __GFP_MOVABLE)
+#define GFP_IOFS	(__GFP_IO | __GFP_FS)
 
 #ifdef CONFIG_NUMA
 #define GFP_THISNODE	(__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
@@ -337,9 +338,7 @@ void drain_local_pages(void *dummy);
 
 extern gfp_t gfp_allowed_mask;
 
-static inline void set_gfp_allowed_mask(gfp_t mask)
-{
-	gfp_allowed_mask = mask;
-}
+extern void set_gfp_allowed_mask(gfp_t mask);
+extern gfp_t clear_gfp_allowed_mask(gfp_t mask);
 
 #endif /* __LINUX_GFP_H */
Index: linux-2.6/init/main.c
===================================================================
--- linux-2.6.orig/init/main.c
+++ linux-2.6/init/main.c
@@ -601,7 +601,7 @@ asmlinkage void __init start_kernel(void
 	local_irq_enable();
 
 	/* Interrupts are enabled now so all GFP allocations are safe. */
-	set_gfp_allowed_mask(__GFP_BITS_MASK);
+	gfp_allowed_mask = __GFP_BITS_MASK;
 
 	kmem_cache_init_late();
 
Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c
+++ linux-2.6/mm/page_alloc.c
@@ -76,6 +76,30 @@ unsigned long totalreserve_pages __read_
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
 
+/*
+ * The following functions are used by the suspend/hibernate code to temporarily
+ * change gfp_allowed_mask in order to avoid using I/O during memory allocations
+ * while devices are suspended.  To avoid races with the suspend/hibernate code,
+ * they should always be called with pm_mutex held (gfp_allowed_mask also should
+ * only be modified with pm_mutex held, unless the suspend/hibernate code is
+ * guaranteed not to run in parallel with that modification).
+ */
+
+void set_gfp_allowed_mask(gfp_t mask)
+{
+	WARN_ON(!mutex_is_locked(&pm_mutex));
+	gfp_allowed_mask = mask;
+}
+
+gfp_t clear_gfp_allowed_mask(gfp_t mask)
+{
+	gfp_t ret = gfp_allowed_mask;
+
+	WARN_ON(!mutex_is_locked(&pm_mutex));
+	gfp_allowed_mask &= ~mask;
+	return ret;
+}
+
 #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
 int pageblock_order __read_mostly;
 #endif
Index: linux-2.6/kernel/power/hibernate.c
===================================================================
--- linux-2.6.orig/kernel/power/hibernate.c
+++ linux-2.6/kernel/power/hibernate.c
@@ -323,6 +323,7 @@ static int create_image(int platform_mod
 int hibernation_snapshot(int platform_mode)
 {
 	int error;
+	gfp_t saved_mask;
 
 	error = platform_begin(platform_mode);
 	if (error)
@@ -334,6 +335,7 @@ int hibernation_snapshot(int platform_mo
 		goto Close;
 
 	suspend_console();
+	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
 	error = dpm_suspend_start(PMSG_FREEZE);
 	if (error)
 		goto Recover_platform;
@@ -351,6 +353,7 @@ int hibernation_snapshot(int platform_mo
 
 	dpm_resume_end(in_suspend ?
 		(error ? PMSG_RECOVER : PMSG_THAW) : PMSG_RESTORE);
+	set_gfp_allowed_mask(saved_mask);
 	resume_console();
  Close:
 	platform_end(platform_mode);
@@ -445,14 +448,17 @@ static int resume_target_kernel(bool pla
 int hibernation_restore(int platform_mode)
 {
 	int error;
+	gfp_t saved_mask;
 
 	pm_prepare_console();
 	suspend_console();
+	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
 	error = dpm_suspend_start(PMSG_QUIESCE);
 	if (!error) {
 		error = resume_target_kernel(platform_mode);
 		dpm_resume_end(PMSG_RECOVER);
 	}
+	set_gfp_allowed_mask(saved_mask);
 	resume_console();
 	pm_restore_console();
 	return error;
@@ -466,6 +472,7 @@ int hibernation_restore(int platform_mod
 int hibernation_platform_enter(void)
 {
 	int error;
+	gfp_t saved_mask;
 
 	if (!hibernation_ops)
 		return -ENOSYS;
@@ -481,6 +488,7 @@ int hibernation_platform_enter(void)
 
 	entering_platform_hibernation = true;
 	suspend_console();
+	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
 	error = dpm_suspend_start(PMSG_HIBERNATE);
 	if (error) {
 		if (hibernation_ops->recover)
@@ -518,6 +526,7 @@ int hibernation_platform_enter(void)
  Resume_devices:
 	entering_platform_hibernation = false;
 	dpm_resume_end(PMSG_RESTORE);
+	set_gfp_allowed_mask(saved_mask);
 	resume_console();
 
  Close:
Index: linux-2.6/kernel/power/suspend.c
===================================================================
--- linux-2.6.orig/kernel/power/suspend.c
+++ linux-2.6/kernel/power/suspend.c
@@ -198,6 +198,7 @@ static int suspend_enter(suspend_state_t
 int suspend_devices_and_enter(suspend_state_t state)
 {
 	int error;
+	gfp_t saved_mask;
 
 	if (!suspend_ops)
 		return -ENOSYS;
@@ -208,6 +209,7 @@ int suspend_devices_and_enter(suspend_st
 			goto Close;
 	}
 	suspend_console();
+	saved_mask = clear_gfp_allowed_mask(GFP_IOFS);
 	suspend_test_start();
 	error = dpm_suspend_start(PMSG_SUSPEND);
 	if (error) {
@@ -224,6 +226,7 @@ int suspend_devices_and_enter(suspend_st
 	suspend_test_start();
 	dpm_resume_end(PMSG_RESUME);
 	suspend_test_finish("resume devices");
+	set_gfp_allowed_mask(saved_mask);
 	resume_console();
  Close:
 	if (suspend_ops->end)
--
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