From 70ffdb9393a7264a069265edded729078dcf0425 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Mon, 11 May 2015 17:52:11 +0200 Subject: mm/fault, arch: Use pagefault_disable() to check for disabled pagefaults in the handler 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 - to detect whether in 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, add a 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. Reviewed-and-tested-by: Thomas Gleixner Signed-off-by: David Hildenbrand Signed-off-by: Peter Zijlstra (Intel) Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: airlied@linux.ie Cc: akpm@linux-foundation.org Cc: benh@kernel.crashing.org Cc: bigeasy@linutronix.de Cc: borntraeger@de.ibm.com Cc: daniel.vetter@intel.com Cc: heiko.carstens@de.ibm.com Cc: herbert@gondor.apana.org.au Cc: hocko@suse.cz Cc: hughd@google.com Cc: mst@redhat.com Cc: paulus@samba.org Cc: ralf@linux-mips.org Cc: schwidefsky@de.ibm.com Cc: yang.shi@windriver.com Link: http://lkml.kernel.org/r/1431359540-32227-7-git-send-email-dahi@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- include/linux/uaccess.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/linux') diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 23290cc93a24..90786d2d74e5 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, -- cgit v1.2.3