[PATCH 2/3] powerpc/mm: handle VM_FAULT_RETRY earlier

Laurent Dufour
2017-02-14T16:45:38Z

In do_page_fault() if handle_mm_fault() returns VM_FAULT_RETRY, retry
the page fault handling before anything else.

This would simplify the handling of the mmap_sem lock in this part of
the code.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
arch/powerpc/mm/fault.c | 67 ++++++++++++++++++++++++++++---------------------
1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index ee09604bbe12..2a6bc7e6e69a 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -434,6 +434,26 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
* the fault.
*/
fault = handle_mm_fault(vma, address, flags);
+
+ /*
+ * Handle the retry right now, the mmap_sem has been released in that
+ * case.
+ */
+ if (unlikely(fault & VM_FAULT_RETRY)) {
+ /* We retry only once */
+ if (flags & FAULT_FLAG_ALLOW_RETRY) {
+ /*
+ * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
+ * of starvation.
+ */
+ flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags |= FAULT_FLAG_TRIED;
+ if (!fatal_signal_pending(current))
+ goto retry;
+ }
+ /* We will enter mm_fault_error() below */
+ }
+
if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
if (fault & VM_FAULT_SIGSEGV)
goto bad_area;
@@ -445,38 +465,27 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
}

/*
- * Major/minor page fault accounting is only done on the
- * initial attempt. If we go through a retry, it is extremely
- * likely that the page will be found in page cache at that point.
+ * Major/minor page fault accounting.
*/
- if (flags & FAULT_FLAG_ALLOW_RETRY) {
- if (fault & VM_FAULT_MAJOR) {
- current->maj_flt++;
- perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
- regs, address);
+ if (fault & VM_FAULT_MAJOR) {
+ current->maj_flt++;
+ perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
+ regs, address);
#ifdef CONFIG_PPC_SMLPAR
- if (firmware_has_feature(FW_FEATURE_CMO)) {
- u32 page_ins;
-
- preempt_disable();
- page_ins = be32_to_cpu(get_lppaca()->page_ins);
- page_ins += 1 << PAGE_FACTOR;
- get_lppaca()->page_ins = cpu_to_be32(page_ins);
- preempt_enable();
- }
-#endif /* CONFIG_PPC_SMLPAR */
- } else {
- current->min_flt++;
- perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
- regs, address);
- }
- if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
- flags |= FAULT_FLAG_TRIED;
- goto retry;
+ if (firmware_has_feature(FW_FEATURE_CMO)) {
+ u32 page_ins;
+
+ preempt_disable();
+ page_ins = be32_to_cpu(get_lppaca()->page_ins);
+ page_ins += 1 << PAGE_FACTOR;
+ get_lppaca()->page_ins = cpu_to_be32(page_ins);
+ preempt_enable();
}
+#endif /* CONFIG_PPC_SMLPAR */
+ } else {
+ current->min_flt++;
+ perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
+ regs, address);
}

up_read(&mm->mmap_sem);
--
2.7.4