[PATCH draft] mm: use pagefault_disable() to check for disabled pagefaults in the handler

From: David Hildenbrand
Date: Thu May 07 2015 - 11:45:48 EST

---- zip ---

This will replacement patch nr 6 if we have an agreement :)

So this is my suggestion to fix the irq context problem. We should not modify
pagefault_disabled() to check for in_atomic(), otherwise we can't reuse it
for might_fault()/might_sleep() checks.

This also allows to clean it up later (if ever :) ).

Thanks!

---- zip ---

Introduce faulthandler_disabled() and use it to check for irq context and
disabled pagefaults (via pagefault_disable()) in the pagefault handlers.

Please note that we keep the in_atomic() checks in place. This is needed
to detect irq context (in which case preemption is always properly disabled).

In contrast, preempt_disable() should never be used to disable pagefaults.
With !CONFIG_PREEMPT_COUNT, preempt_disable() doesn't modify the preempt
counter, and therefore the result of in_atomic() differs.
We validate that condition by using might_fault() checks when calling
might_sleep().

Therefore, we add an comment to faulthandler_disabled(), describing why this
is needed.

faulthandler_disabled() and pagefault_disable() are defined in
linux/uaccess.h, so let's properly add that include to all relevant files.

This patch is based on a patch from Thomas Gleixner.

Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
---
arch/alpha/mm/fault.c | 5 ++---
arch/arc/mm/fault.c | 2 +-
arch/arm/mm/fault.c | 2 +-
arch/arm64/mm/fault.c | 2 +-
arch/avr32/mm/fault.c | 4 ++--
arch/cris/mm/fault.c | 6 +++---
arch/frv/mm/fault.c | 4 ++--
arch/ia64/mm/fault.c | 4 ++--
arch/m32r/mm/fault.c | 8 ++++----
arch/m68k/mm/fault.c | 4 ++--
arch/metag/mm/fault.c | 2 +-
arch/microblaze/mm/fault.c | 8 ++++----
arch/mips/mm/fault.c | 4 ++--
arch/mn10300/mm/fault.c | 4 ++--
arch/nios2/mm/fault.c | 2 +-
arch/parisc/kernel/traps.c | 4 ++--
arch/parisc/mm/fault.c | 4 ++--
arch/powerpc/mm/fault.c | 9 +++++----
arch/s390/mm/fault.c | 2 +-
arch/score/mm/fault.c | 3 ++-
arch/sh/mm/fault.c | 5 +++--
arch/sparc/mm/fault_32.c | 4 ++--
arch/sparc/mm/fault_64.c | 4 ++--
arch/sparc/mm/init_64.c | 2 +-
arch/tile/mm/fault.c | 4 ++--
arch/um/kernel/trap.c | 4 ++--
arch/unicore32/mm/fault.c | 2 +-
arch/x86/mm/fault.c | 5 +++--
arch/xtensa/mm/fault.c | 4 ++--
include/linux/uaccess.h | 12 ++++++++++++
30 files changed, 72 insertions(+), 57 deletions(-)

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index 9d0ac09..4a905bd 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -23,8 +23,7 @@
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/module.h>
-
-#include <asm/uaccess.h>
+#include <linux/uaccess.h>

extern void die_if_kernel(char *,struct pt_regs *,long, unsigned long *);

@@ -107,7 +106,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,

/* If we're in an interrupt context, or have no user context,
we must not take the fault. */
- if (!mm || in_atomic())
+ if (!mm || faulthandler_disabled())
goto no_context;

#ifdef CONFIG_ALPHA_LARGE_VMALLOC
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 6a2e006..d948e4e 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -86,7 +86,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 6333d9c..0d629b8 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -276,7 +276,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 96da131..0948d32 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -211,7 +211,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
* If we're in an interrupt or have no user context, we must not take
* the fault.
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/avr32/mm/fault.c b/arch/avr32/mm/fault.c
index d223a8b..c035339 100644
--- a/arch/avr32/mm/fault.c
+++ b/arch/avr32/mm/fault.c
@@ -14,11 +14,11 @@
#include <linux/pagemap.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>
+#include <linux/uaccess.h>

#include <asm/mmu_context.h>
#include <asm/sysreg.h>
#include <asm/tlb.h>
-#include <asm/uaccess.h>

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, int trap)
@@ -81,7 +81,7 @@ asmlinkage void do_page_fault(unsigned long ecr, struct pt_regs *regs)
* If we're in an interrupt or have no user context, we must
* not take the fault...
*/
- if (in_atomic() || !mm || regs->sr & SYSREG_BIT(GM))
+ if (faulthandler_disabled() || !mm || regs->sr & SYSREG_BIT(GM))
goto no_context;

local_irq_enable();
diff --git a/arch/cris/mm/fault.c b/arch/cris/mm/fault.c
index 83f12f2..3066d40 100644
--- a/arch/cris/mm/fault.c
+++ b/arch/cris/mm/fault.c
@@ -8,7 +8,7 @@
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/wait.h>
-#include <asm/uaccess.h>
+#include <linux/uaccess.h>
#include <arch/system.h>

extern int find_fixup_code(struct pt_regs *);
@@ -109,11 +109,11 @@ do_page_fault(unsigned long address, struct pt_regs *regs,
info.si_code = SEGV_MAPERR;

/*
- * If we're in an interrupt or "atomic" operation or have no
+ * If we're in an interrupt, have pagefaults disabled or have no
* user context, we must not take the fault.
*/

- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/frv/mm/fault.c b/arch/frv/mm/fault.c
index ec4917d..61d9976 100644
--- a/arch/frv/mm/fault.c
+++ b/arch/frv/mm/fault.c
@@ -19,9 +19,9 @@
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/hardirq.h>
+#include <linux/uaccess.h>

#include <asm/pgtable.h>
-#include <asm/uaccess.h>
#include <asm/gdb-stub.h>

/*****************************************************************************/
@@ -78,7 +78,7 @@ asmlinkage void do_page_fault(int datammu, unsigned long esr0, unsigned long ear
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(__frame))
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index ba5ba7a..70b40d1 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -11,10 +11,10 @@
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/prefetch.h>
+#include <linux/uaccess.h>

#include <asm/pgtable.h>
#include <asm/processor.h>
-#include <asm/uaccess.h>

extern int die(char *, struct pt_regs *, long);

@@ -96,7 +96,7 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
/*
* If we're in an interrupt or have no user context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

#ifdef CONFIG_VIRTUAL_MEM_MAP
diff --git a/arch/m32r/mm/fault.c b/arch/m32r/mm/fault.c
index e3d4d48901..8f9875b 100644
--- a/arch/m32r/mm/fault.c
+++ b/arch/m32r/mm/fault.c
@@ -24,9 +24,9 @@
#include <linux/vt_kern.h> /* For unblank_screen() */
#include <linux/highmem.h>
#include <linux/module.h>
+#include <linux/uaccess.h>

#include <asm/m32r.h>
-#include <asm/uaccess.h>
#include <asm/hardirq.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
@@ -111,10 +111,10 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code,
mm = tsk->mm;

/*
- * If we're in an interrupt or have no user context or are running in an
- * atomic region then we must not take the fault..
+ * If we're in an interrupt or have no user context or have pagefaults
+ * disabled then we must not take the fault.
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto bad_area_nosemaphore;

if (error_code & ACE_USERMODE)
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index b2f04ae..6a94cdd 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -10,10 +10,10 @@
#include <linux/ptrace.h>
#include <linux/interrupt.h>
#include <linux/module.h>
+#include <linux/uaccess.h>

#include <asm/setup.h>
#include <asm/traps.h>
-#include <asm/uaccess.h>
#include <asm/pgalloc.h>

extern void die_if_kernel(char *, struct pt_regs *, long);
@@ -81,7 +81,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/metag/mm/fault.c b/arch/metag/mm/fault.c
index 2de5dc6..f57edca 100644
--- a/arch/metag/mm/fault.c
+++ b/arch/metag/mm/fault.c
@@ -105,7 +105,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,

mm = tsk->mm;

- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index d46a5eb..177dfc0 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -107,14 +107,14 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
is_write = 0;

- if (unlikely(in_atomic() || !mm)) {
+ if (unlikely(faulthandler_disabled() || !mm)) {
if (kernel_mode(regs))
goto bad_area_nosemaphore;

- /* in_atomic() in user mode is really bad,
+ /* faulthandler_disabled() in user mode is really bad,
as is current->mm == NULL. */
- pr_emerg("Page fault in user mode with in_atomic(), mm = %p\n",
- mm);
+ pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n",
+ mm);
pr_emerg("r15 = %lx MSR = %lx\n",
regs->r15, regs->msr);
die("Weird page fault", regs, SIGSEGV);
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index 7ff8637..36c0f26 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -21,10 +21,10 @@
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/perf_event.h>
+#include <linux/uaccess.h>

#include <asm/branch.h>
#include <asm/mmu_context.h>
-#include <asm/uaccess.h>
#include <asm/ptrace.h>
#include <asm/highmem.h> /* For VMALLOC_END */
#include <linux/kdebug.h>
@@ -94,7 +94,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto bad_area_nosemaphore;

if (user_mode(regs))
diff --git a/arch/mn10300/mm/fault.c b/arch/mn10300/mm/fault.c
index 0c2cc5d..4a1d181 100644
--- a/arch/mn10300/mm/fault.c
+++ b/arch/mn10300/mm/fault.c
@@ -23,8 +23,8 @@
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/vt_kern.h> /* For unblank_screen() */
+#include <linux/uaccess.h>

-#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/hardirq.h>
#include <asm/cpu-regs.h>
@@ -168,7 +168,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long fault_code,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if ((fault_code & MMUFCR_xFC_ACCESS) == MMUFCR_xFC_ACCESS_USR)
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index 0c9b6af..b51878b 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -77,7 +77,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto bad_area_nosemaphore;

if (user_mode(regs))
diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index 47ee620..6548fd1 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -26,9 +26,9 @@
#include <linux/console.h>
#include <linux/bug.h>
#include <linux/ratelimit.h>
+#include <linux/uaccess.h>

#include <asm/assembly.h>
-#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/traps.h>
@@ -800,7 +800,7 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
* unless pagefault_disable() was called before.
*/

- if (fault_space == 0 && !in_atomic())
+ if (fault_space == 0 && !faulthandler_disabled())
{
pdc_chassis_send_status(PDC_CHASSIS_DIRECT_PANIC);
parisc_terminate("Kernel Fault", regs, code, fault_address);
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index e5120e6..15503ad 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -15,8 +15,8 @@
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/module.h>
+#include <linux/uaccess.h>

-#include <asm/uaccess.h>
#include <asm/traps.h>

/* Various important other fields */
@@ -207,7 +207,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
int fault;
unsigned int flags;

- if (in_atomic())
+ if (pagefault_disabled())
goto no_context;

tsk = current;
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index b396868..6d53597 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -33,13 +33,13 @@
#include <linux/ratelimit.h>
#include <linux/context_tracking.h>
#include <linux/hugetlb.h>
+#include <linux/uaccess.h>

#include <asm/firmware.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
-#include <asm/uaccess.h>
#include <asm/tlbflush.h>
#include <asm/siginfo.h>
#include <asm/debug.h>
@@ -272,15 +272,16 @@ int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
if (!arch_irq_disabled_regs(regs))
local_irq_enable();

- if (in_atomic() || mm == NULL) {
+ if (faulthandler_disabled() || mm == NULL) {
if (!user_mode(regs)) {
rc = SIGSEGV;
goto bail;
}
- /* in_atomic() in user mode is really bad,
+ /* faulthandler_disabled() in user mode is really bad,
as is current->mm == NULL. */
printk(KERN_EMERG "Page fault in user mode with "
- "in_atomic() = %d mm = %p\n", in_atomic(), mm);
+ "faulthandler_disabled() = %d mm = %p\n",
+ faulthandler_disabled(), mm);
printk(KERN_EMERG "NIP = %lx MSR = %lx\n",
regs->nip, regs->msr);
die("Weird page fault", regs, SIGSEGV);
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 76515bc..4c8f5d7 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -399,7 +399,7 @@ static inline int do_exception(struct pt_regs *regs, int access)
* user context.
*/
fault = VM_FAULT_BADCONTEXT;
- if (unlikely(!user_space_fault(regs) || in_atomic() || !mm))
+ if (unlikely(!user_space_fault(regs) || faulthandler_disabled() || !mm))
goto out;

address = trans_exc_code & __FAIL_ADDR_MASK;
diff --git a/arch/score/mm/fault.c b/arch/score/mm/fault.c
index 6860beb..37a6c2e 100644
--- a/arch/score/mm/fault.c
+++ b/arch/score/mm/fault.c
@@ -34,6 +34,7 @@
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
+#include <linux/uaccess.h>

/*
* This routine handles page faults. It determines the address,
@@ -73,7 +74,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long write,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (pagefault_disabled() || !mm)
goto bad_area_nosemaphore;

if (user_mode(regs))
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index a58fec9..79d8276 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -17,6 +17,7 @@
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/kdebug.h>
+#include <linux/uaccess.h>
#include <asm/io_trapped.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
@@ -438,9 +439,9 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,

/*
* If we're in an interrupt, have no user context or are running
- * in an atomic region then we must not take the fault:
+ * with pagefaults disabled then we must not take the fault:
*/
- if (unlikely(in_atomic() || !mm)) {
+ if (unlikely(faulthandler_disabled() || !mm)) {
bad_area_nosemaphore(regs, error_code, address);
return;
}
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 70d8171..c399e7b 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -21,6 +21,7 @@
#include <linux/perf_event.h>
#include <linux/interrupt.h>
#include <linux/kdebug.h>
+#include <linux/uaccess.h>

#include <asm/page.h>
#include <asm/pgtable.h>
@@ -29,7 +30,6 @@
#include <asm/setup.h>
#include <asm/smp.h>
#include <asm/traps.h>
-#include <asm/uaccess.h>

#include "mm_32.h"

@@ -196,7 +196,7 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (pagefault_disabled() || !mm)
goto no_context;

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 4798232..e9268ea 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -22,12 +22,12 @@
#include <linux/kdebug.h>
#include <linux/percpu.h>
#include <linux/context_tracking.h>
+#include <linux/uaccess.h>

#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/openprom.h>
#include <asm/oplib.h>
-#include <asm/uaccess.h>
#include <asm/asi.h>
#include <asm/lsu.h>
#include <asm/sections.h>
@@ -330,7 +330,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto intr_or_no_mm;

perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index 4ca0d6b..cee9b77 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -2706,7 +2706,7 @@ void hugetlb_setup(struct pt_regs *regs)
struct mm_struct *mm = current->mm;
struct tsb_config *tp;

- if (in_atomic() || !mm) {
+ if (faulthandler_disabled() || !mm) {
const struct exception_table_entry *entry;

entry = search_exception_tables(regs->tpc);
diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index e83cc99..3f4f58d 100644
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -354,9 +354,9 @@ static int handle_page_fault(struct pt_regs *regs,

/*
* If we're in an interrupt, have no user context or are running in an
- * atomic region then we must not take the fault.
+ * region with pagefaults disabled then we must not take the fault.
*/
- if (in_atomic() || !mm) {
+ if (pagefault_disabled() || !mm) {
vma = NULL; /* happy compiler */
goto bad_area_nosemaphore;
}
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 8e4daf4..f9c9e5a 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -35,10 +35,10 @@ int handle_page_fault(unsigned long address, unsigned long ip,
*code_out = SEGV_MAPERR;

/*
- * If the fault was during atomic operation, don't take the fault, just
+ * If the fault was with pagefaults disabled, don't take the fault, just
* fail.
*/
- if (in_atomic())
+ if (faulthandler_disabled())
goto out_nosemaphore;

if (is_user)
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index 0dc922d..afccef552 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -218,7 +218,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm)
+ if (faulthandler_disabled() || !mm)
goto no_context;

if (user_mode(regs))
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 181c53b..9dc9098 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -13,6 +13,7 @@
#include <linux/hugetlb.h> /* hstate_index_to_shift */
#include <linux/prefetch.h> /* prefetchw */
#include <linux/context_tracking.h> /* exception_enter(), ... */
+#include <linux/uaccess.h> /* faulthandler_disabled() */

#include <asm/traps.h> /* dotraplinkage, ... */
#include <asm/pgalloc.h> /* pgd_*(), ... */
@@ -1126,9 +1127,9 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,

/*
* If we're in an interrupt, have no user context or are running
- * in an atomic region then we must not take the fault:
+ * in a region with pagefaults disabled then we must not take the fault
*/
- if (unlikely(in_atomic() || !mm)) {
+ if (unlikely(faulthandler_disabled() || !mm)) {
bad_area_nosemaphore(regs, error_code, address);
return;
}
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index 9e3571a..83a44a3 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -15,10 +15,10 @@
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/hardirq.h>
+#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/hardirq.h>
-#include <asm/uaccess.h>
#include <asm/pgalloc.h>

DEFINE_PER_CPU(unsigned long, asid_cache) = ASID_USER_FIRST;
@@ -57,7 +57,7 @@ void do_page_fault(struct pt_regs *regs)
/* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
- if (in_atomic() || !mm) {
+ if (faulthandler_disabled() || !mm) {
bad_page_fault(regs, address, SIGSEGV);
return;
}
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 23290cc..90786d2 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -59,6 +59,18 @@ static inline void pagefault_enable(void)
*/
#define pagefault_disabled() (current->pagefault_disabled != 0)

+/*
+ * The pagefault handler is in general disabled by pagefault_disable() or
+ * when in irq context (via in_atomic()).
+ *
+ * This function should only be used by the fault handlers. Other users should
+ * stick to pagefault_disabled().
+ * Please NEVER use preempt_disable() to disable the fault handler. With
+ * !CONFIG_PREEMPT_COUNT, this is like a NOP. So the handler won't be disabled.
+ * in_atomic() will report different values based on !CONFIG_PREEMPT_COUNT.
+ */
+#define faulthandler_disabled() (pagefault_disabled() || in_atomic())
+
#ifndef ARCH_HAS_NOCACHE_UACCESS

static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
--
2.1.4

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