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Commit 3a13c4d7 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

x86: finish user fault error path with fatal signal 



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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: azurIt <azurit@pobox.sk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 759496ba

arch/x86/mm/fault.c

+17 −18
Original line number Diff line number Diff line
@@ -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))

	if (fatal_signal_pending(current) && !(error_code & PF_USER)) {

		up_read(&current->mm->mmap_sem);

		if (!(error_code & PF_USER))

		no_context(regs, error_code, address, 0, 0);

		return 1;

		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(&current->mm->mmap_sem);

			no_context(regs, error_code, address,

				   SIGSEGV, SEGV_MAPERR);

			return 1;

			return;

		}



		up_read(&current->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)
@@ -1189,8 +1180,16 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code) 
	 */

	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))

	/*

	 * 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;

	}