This was triggered by investigation of a deadlock after OOM killer invocation,
see [1] for more details.
Looks like our handling of fatal signal in do_page_fault() has some issues:
1. We only want to do special (read "early") handling of fatal signal
if handle_mm_fault() returned VM_FAULT_RETRY so that we don't loop
in retry loop endlessly, otherwise we'll handle that signal normally
on exit from exception handler.
2. up_read() is not needed as indeed it will be done in __lock_page_or_retry()
in mm/filemap.c.
With above comments in mind simplified version should be like that:
------------------------------->8---------------------------
if (fatal_signal_pending(current)
if (fault & VM_FAULT_RETRY)
if (user_mode(regs))
return;
------------------------------->8---------------------------
But looks like there's a room for improvement, see [2].
Instead of proceeding forward and then inevitably hitting retry path we
short-cut right to kernel fix-up code in no_context.
[1]
http://lists.infradead.org/pipermail/linux-snps-arc/2018-February/003403.html
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=746a272e44141af24a02f6c9b0f65f4c4598ed42
Signed-off-by: Alexey Brodkin <abrod...@synopsys.com>
---
arch/arc/mm/fault.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index a0b7bd6d030d..17ed78e2f5eb 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -139,12 +139,16 @@ void do_page_fault(unsigned long address, struct pt_regs
*regs)
*/
fault = handle_mm_fault(vma, address, flags);
- /* If Pagefault was interrupted by SIGKILL, exit page fault "early" */
+ /* 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(fatal_signal_pending(current))) {
- if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
- up_read(&mm->mmap_sem);
- if (user_mode(regs))
+ if (fault & VM_FAULT_RETRY) {
+ if (!user_mode(regs))
+ goto no_context;
return;
+ }
}
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
--
2.17.1
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