From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752936Ab3HCRAp (ORCPT ); Sat, 3 Aug 2013 13:00:45 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:51749 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752832Ab3HCRAj (ORCPT ); Sat, 3 Aug 2013 13:00:39 -0400 From: Johannes Weiner To: Andrew Morton Cc: Michal Hocko , David Rientjes , KAMEZAWA Hiroyuki , azurIt , KOSAKI Motohiro , linux-mm@kvack.org, cgroups@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [patch 4/7] x86: finish user fault error path with fatal signal Date: Sat, 3 Aug 2013 12:59:57 -0400 Message-Id: <1375549200-19110-5-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 1.8.3.2 In-Reply-To: <1375549200-19110-1-git-send-email-hannes@cmpxchg.org> References: <1375549200-19110-1-git-send-email-hannes@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The x86 fault handler bails in the middle of error handling when the task has a fatal signal pending. For a subsequent patch this is a problem in OOM situations because it relies on pagefault_out_of_memory() being called even when the task has been killed, to perform proper per-task OOM state unwinding. Shortcutting the fault like this is a rather minor optimization that saves a few instructions in rare cases. Just remove it for user-triggered faults. Use the opportunity to split the fault retry handling from actual fault errors and add locking documentation that reads suprisingly similar to ARM's. Signed-off-by: Johannes Weiner Reviewed-by: Michal Hocko Acked-by: KOSAKI Motohiro --- arch/x86/mm/fault.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 6d77c38..3aaeffc 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -842,23 +842,15 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, force_sig_info_fault(SIGBUS, code, address, tsk, fault); } -static noinline int +static noinline void mm_fault_error(struct pt_regs *regs, unsigned long error_code, unsigned long address, unsigned int fault) { - /* - * Pagefault was interrupted by SIGKILL. We have no reason to - * continue pagefault. - */ - if (fatal_signal_pending(current)) { - if (!(fault & VM_FAULT_RETRY)) - up_read(¤t->mm->mmap_sem); - if (!(error_code & PF_USER)) - no_context(regs, error_code, address, 0, 0); - return 1; + if (fatal_signal_pending(current) && !(error_code & PF_USER)) { + up_read(¤t->mm->mmap_sem); + no_context(regs, error_code, address, 0, 0); + return; } - if (!(fault & VM_FAULT_ERROR)) - return 0; if (fault & VM_FAULT_OOM) { /* Kernel mode? Handle exceptions or die: */ @@ -866,7 +858,7 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code, up_read(¤t->mm->mmap_sem); no_context(regs, error_code, address, SIGSEGV, SEGV_MAPERR); - return 1; + return; } up_read(¤t->mm->mmap_sem); @@ -884,7 +876,6 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code, else BUG(); } - return 1; } static int spurious_fault_check(unsigned long error_code, pte_t *pte) @@ -1189,9 +1180,17 @@ good_area: */ fault = handle_mm_fault(mm, vma, address, flags); - if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) { - if (mm_fault_error(regs, error_code, address, fault)) - return; + /* + * If we need to retry but a fatal signal is pending, handle the + * signal first. We do not need to release the mmap_sem because it + * would already be released in __lock_page_or_retry in mm/filemap.c. + */ + if (unlikely((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))) + return; + + if (unlikely(fault & VM_FAULT_ERROR)) { + mm_fault_error(regs, error_code, address, fault); + return; } /* -- 1.8.3.2 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: [patch 4/7] x86: finish user fault error path with fatal signal Date: Sat, 3 Aug 2013 12:59:57 -0400 Message-ID: <1375549200-19110-5-git-send-email-hannes@cmpxchg.org> References: <1375549200-19110-1-git-send-email-hannes@cmpxchg.org> Return-path: In-Reply-To: <1375549200-19110-1-git-send-email-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Michal Hocko , David Rientjes , KAMEZAWA Hiroyuki , azurIt , KOSAKI Motohiro , linux-mm@kvack.org, cgroups@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org The x86 fault handler bails in the middle of error handling when the task has a fatal signal pending. For a subsequent patch this is a problem in OOM situations because it relies on pagefault_out_of_memory() being called even when the task has been killed, to perform proper per-task OOM state unwinding. Shortcutting the fault like this is a rather minor optimization that saves a few instructions in rare cases. Just remove it for user-triggered faults. Use the opportunity to split the fault retry handling from actual fault errors and add locking documentation that reads suprisingly similar to ARM's. Signed-off-by: Johannes Weiner Reviewed-by: Michal Hocko Acked-by: KOSAKI Motohiro --- arch/x86/mm/fault.c | 35 +++++++++++++++++------------------ 1 file changed, 17 insertions(+), 18 deletions(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 6d77c38..3aaeffc 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -842,23 +842,15 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, force_sig_info_fault(SIGBUS, code, address, tsk, fault); } -static noinline int +static noinline void mm_fault_error(struct pt_regs *regs, unsigned long error_code, unsigned long address, unsigned int fault) { - /* - * Pagefault was interrupted by SIGKILL. We have no reason to - * continue pagefault. - */ - if (fatal_signal_pending(current)) { - if (!(fault & VM_FAULT_RETRY)) - up_read(¤t->mm->mmap_sem); - if (!(error_code & PF_USER)) - no_context(regs, error_code, address, 0, 0); - return 1; + if (fatal_signal_pending(current) && !(error_code & PF_USER)) { + up_read(¤t->mm->mmap_sem); + no_context(regs, error_code, address, 0, 0); + return; } - if (!(fault & VM_FAULT_ERROR)) - return 0; if (fault & VM_FAULT_OOM) { /* Kernel mode? Handle exceptions or die: */ @@ -866,7 +858,7 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code, up_read(¤t->mm->mmap_sem); no_context(regs, error_code, address, SIGSEGV, SEGV_MAPERR); - return 1; + return; } up_read(¤t->mm->mmap_sem); @@ -884,7 +876,6 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code, else BUG(); } - return 1; } static int spurious_fault_check(unsigned long error_code, pte_t *pte) @@ -1189,9 +1180,17 @@ good_area: */ fault = handle_mm_fault(mm, vma, address, flags); - if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) { - if (mm_fault_error(regs, error_code, address, fault)) - return; + /* + * If we need to retry but a fatal signal is pending, handle the + * signal first. We do not need to release the mmap_sem because it + * would already be released in __lock_page_or_retry in mm/filemap.c. + */ + if (unlikely((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))) + return; + + if (unlikely(fault & VM_FAULT_ERROR)) { + mm_fault_error(regs, error_code, address, fault); + return; } /* -- 1.8.3.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org