Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757754AbaLJOYk (ORCPT ); Wed, 10 Dec 2014 09:24:40 -0500 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:49365 "EHLO e06smtp13.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757610AbaLJOXp (ORCPT ); Wed, 10 Dec 2014 09:23:45 -0500 From: David Hildenbrand To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Cc: benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, heiko.carstens@de.ibm.com, dahi@linux.vnet.ibm.com, schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de, David.Laight@ACULAB.COM, peterz@infradead.org, hughd@google.com, hocko@suse.cz Subject: [PATCH v2 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled Date: Wed, 10 Dec 2014 15:23:32 +0100 Message-Id: <1418221414-60110-4-git-send-email-dahi@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.5.5 In-Reply-To: <1418221414-60110-1-git-send-email-dahi@linux.vnet.ibm.com> References: <1418221414-60110-1-git-send-email-dahi@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14121014-0013-0000-0000-0000022A7160 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 662bbcb2747c ("mm, sched: Allow uaccess in atomic with pagefault_disable()") removed might_sleep() checks for all user access code (that uses might_fault()). The reason was to disable wrong "sleep in atomic" warnings in the following scenario: pagefault_disable() rc = copy_to_user(...) pagefault_enable() Which is valid, as pagefault_disable() increments the preempt counter and therefore disables the pagefault handler. copy_to_user() will not sleep and return an invalid return code if a page is not available. However, as all might_sleep() checks are removed, CONFIG_DEBUG_ATOMIC_SLEEP would no longer detect the following scenario: spin_lock(&lock); rc = copy_to_user(...) spin_unlock(&lock) If the kernel is compiled with preemption turned on, the preempt counter would be incremented and copy_to_user() would never sleep. However, with preemption turned off, the preempt counter will not be touched, we will therefore sleep in atomic context. We really want to enable CONFIG_DEBUG_ATOMIC_SLEEP checks for user access functions again, otherwise horrible deadlocks might be hard to debug. Root of all evil is that pagefault_disable() acted almost as preempt_disable(), depending on preemption being turned on/off. As we now have pagefault_disabled(), we can use it to distingusih whether user acces functions might sleep. Convert might_fault() into a makro that calls __might_fault(), to allow proper file + line messages in case of a might_sleep() warning. We can't move the code directly into kernel.h for now, as that results in ugly header recursions we can't avoid for now. Signed-off-by: David Hildenbrand --- include/linux/kernel.h | 3 ++- mm/memory.c | 18 ++++++------------ 2 files changed, 8 insertions(+), 13 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 446d76a..7e65a55 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -232,7 +232,8 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro) #if defined(CONFIG_MMU) && \ (defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)) -void might_fault(void); +#define might_fault() __might_fault(__FILE__, __LINE__) +void __might_fault(const char *file, int line); #else static inline void might_fault(void) { } #endif diff --git a/mm/memory.c b/mm/memory.c index 0b3f6c7..563720a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3686,7 +3686,7 @@ void print_vma_addr(char *prefix, unsigned long ip) } #if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP) -void might_fault(void) +void __might_fault(const char *file, int line) { /* * Some code (nfs/sunrpc) uses socket ops on kernel memory while @@ -3696,21 +3696,15 @@ void might_fault(void) */ if (segment_eq(get_fs(), KERNEL_DS)) return; - - /* - * it would be nicer only to annotate paths which are not under - * pagefault_disable, however that requires a larger audit and - * providing helpers like get_user_atomic. - */ - if (in_atomic()) + if (pagefault_disabled()) return; - - __might_sleep(__FILE__, __LINE__, 0); - + __might_sleep(file, line, 0); +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) if (current->mm) might_lock_read(¤t->mm->mmap_sem); +#endif } -EXPORT_SYMBOL(might_fault); +EXPORT_SYMBOL(__might_fault); #endif #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS) -- 1.8.5.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/