The patch titled
Subject: mm,hugetlb: simplify error handling in hugetlb_cow()
has been added to the -mm tree. Its filename is
mmhugetlb-simplify-error-handling-in-hugetlb_cow.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmhugetlb-simplify-error-handling-in-hugetlb_cow.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmhugetlb-simplify-error-handling-in-hugetlb_cow.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Davidlohr Bueso <davidlohr@xxxxxx>
Subject: mm,hugetlb: simplify error handling in hugetlb_cow()
When returning from hugetlb_cow(), we always (1) put back the refcount for
each referenced page -- always 'old', and 'new' if allocation was
successful. And (2) retake the page table lock right before returning, as
the callers expects. This logic can be simplified and encapsulated, as
proposed in this patch. In addition to cleaner code, we also shave a few
bytes off the instruction text:
text data bss dec hex filename
28399 462 41328 70189 1122d mm/hugetlb.o-baseline
28367 462 41328 70157 1120d mm/hugetlb.o-patched
Passes libhugetlbfs testcases.
Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Cc: Aswin Chandramouleeswaran <aswin@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 35 ++++++++++++++++-------------------
1 file changed, 16 insertions(+), 19 deletions(-)
diff -puN mm/hugetlb.c~mmhugetlb-simplify-error-handling-in-hugetlb_cow mm/hugetlb.c
--- a/mm/hugetlb.c~mmhugetlb-simplify-error-handling-in-hugetlb_cow
+++ a/mm/hugetlb.c
@@ -2808,7 +2808,7 @@ static int hugetlb_cow(struct mm_struct
{
struct hstate *h = hstate_vma(vma);
struct page *old_page, *new_page;
- int outside_reserve = 0;
+ int ret = 0, outside_reserve = 0;
unsigned long mmun_start; /* For mmu_notifiers */
unsigned long mmun_end; /* For mmu_notifiers */
@@ -2838,14 +2838,14 @@ retry_avoidcopy:
page_cache_get(old_page);
- /* Drop page table lock as buddy allocator may be called */
+ /*
+ * Drop page table lock as buddy allocator may be called. It will
+ * be acquired again before returning to the caller, as expected.
+ */
spin_unlock(ptl);
new_page = alloc_huge_page(vma, address, outside_reserve);
if (IS_ERR(new_page)) {
- long err = PTR_ERR(new_page);
- page_cache_release(old_page);
-
/*
* If a process owning a MAP_PRIVATE mapping fails to COW,
* it is due to references held by a child and an insufficient
@@ -2854,6 +2854,7 @@ retry_avoidcopy:
* may get SIGKILLed if it later faults.
*/
if (outside_reserve) {
+ page_cache_release(old_page);
BUG_ON(huge_pte_none(pte));
unmap_ref_private(mm, vma, old_page, address);
BUG_ON(huge_pte_none(pte));
@@ -2869,12 +2870,9 @@ retry_avoidcopy:
return 0;
}
- /* Caller expects lock to be held */
- spin_lock(ptl);
- if (err == -ENOMEM)
- return VM_FAULT_OOM;
- else
- return VM_FAULT_SIGBUS;
+ ret = (PTR_ERR(new_page) == -ENOMEM) ?
+ VM_FAULT_OOM : VM_FAULT_SIGBUS;
+ goto out_release_old;
}
/*
@@ -2882,11 +2880,8 @@ retry_avoidcopy:
* anon_vma prepared.
*/
if (unlikely(anon_vma_prepare(vma))) {
- page_cache_release(new_page);
- page_cache_release(old_page);
- /* Caller expects lock to be held */
- spin_lock(ptl);
- return VM_FAULT_OOM;
+ ret = VM_FAULT_OOM;
+ goto out_release_all;
}
copy_user_huge_page(new_page, old_page, address, vma,
@@ -2896,6 +2891,7 @@ retry_avoidcopy:
mmun_start = address & huge_page_mask(h);
mmun_end = mmun_start + huge_page_size(h);
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
/*
* Retake the page table lock to check for racing updates
* before the page tables are altered
@@ -2916,12 +2912,13 @@ retry_avoidcopy:
}
spin_unlock(ptl);
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+out_release_all:
page_cache_release(new_page);
+out_release_old:
page_cache_release(old_page);
- /* Caller expects lock to be held */
- spin_lock(ptl);
- return 0;
+ spin_lock(ptl); /* Caller expects lock to be held */
+ return ret;
}
/* Return the pagecache page at a given address within a VMA */
_
Patches currently in -mm which might be from davidlohr@xxxxxx are
tools-msgque-improve-error-handling-when-not-running-as-root.patch
mmhugetlb-make-unmap_ref_private-return-void.patch
mmhugetlb-simplify-error-handling-in-hugetlb_cow.patch
m68k-call-find_vma-with-the-mmap_sem-held-in-sys_cacheflush.patch
zram-remove-global-tb_lock-with-fine-grain-lock.patch
printk-make-dynamic-kernel-ring-buffer-alignment-explicit.patch
printk-move-power-of-2-practice-of-ring-buffer-size-to-a-helper.patch
printk-make-dynamic-units-clear-for-the-kernel-ring-buffer.patch
printk-allow-increasing-the-ring-buffer-depending-on-the-number-of-cpus.patch
shm-make-exit_shm-work-proportional-to-task-activity.patch
shm-allow-exit_shm-in-parallel-if-only-marking-orphans.patch
shm-remove-unneeded-extern-for-function.patch
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