The patch titled
Subject: hugetlbfs: remove unnecessary code after i_mmap_rwsem synchronization
has been added to the -mm tree. Its filename is
hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization.patch
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: hugetlbfs: remove unnecessary code after i_mmap_rwsem synchronization
After expanding i_mmap_rwsem use for better shared pmd and page fault/
truncation synchronization, remove code that is no longer necessary.
Link: http://lkml.kernel.org/r/20181203200850.6460-4-mike.kravetz@xxxxxxxxxx
Fixes: ebed4bfc8da8 ("hugetlb: fix absurd HugePages_Rsvd")
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 46 +++++++++++++----------------------------
mm/hugetlb.c | 21 ++++++++----------
2 files changed, 25 insertions(+), 42 deletions(-)
--- a/fs/hugetlbfs/inode.c~hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization
+++ a/fs/hugetlbfs/inode.c
@@ -383,17 +383,16 @@ hugetlb_vmdelete_list(struct rb_root_cac
* truncation is indicated by end of range being LLONG_MAX
* In this case, we first scan the range and release found pages.
* After releasing pages, hugetlb_unreserve_pages cleans up region/reserv
- * maps and global counts. Page faults can not race with truncation
- * in this routine. hugetlb_no_page() prevents page faults in the
- * truncated range. It checks i_size before allocation, and again after
- * with the page table lock for the page held. The same lock must be
- * acquired to unmap a page.
+ * maps and global counts.
* hole punch is indicated if end is not LLONG_MAX
* In the hole punch case we scan the range and release found pages.
* Only when releasing a page is the associated region/reserv map
* deleted. The region/reserv map for ranges without associated
- * pages are not modified. Page faults can race with hole punch.
- * This is indicated if we find a mapped page.
+ * pages are not modified.
+ *
+ * Callers of this routine must hold the i_mmap_rwsem in write mode to prevent
+ * races with page faults.
+ *
* Note: If the passed end of range value is beyond the end of file, but
* not LLONG_MAX this routine still performs a hole punch operation.
*/
@@ -423,32 +422,14 @@ static void remove_inode_hugepages(struc
for (i = 0; i < pagevec_count(&pvec); ++i) {
struct page *page = pvec.pages[i];
- u32 hash;
index = page->index;
- hash = hugetlb_fault_mutex_hash(h, current->mm,
- &pseudo_vma,
- mapping, index, 0);
- mutex_lock(&hugetlb_fault_mutex_table[hash]);
-
/*
- * If page is mapped, it was faulted in after being
- * unmapped in caller. Unmap (again) now after taking
- * the fault mutex. The mutex will prevent faults
- * until we finish removing the page.
- *
- * This race can only happen in the hole punch case.
- * Getting here in a truncate operation is a bug.
+ * A mapped page is impossible as callers should unmap
+ * all references before calling. And, i_mmap_rwsem
+ * prevents the creation of additional mappings.
*/
- if (unlikely(page_mapped(page))) {
- BUG_ON(truncate_op);
-
- i_mmap_lock_write(mapping);
- hugetlb_vmdelete_list(&mapping->i_mmap,
- index * pages_per_huge_page(h),
- (index + 1) * pages_per_huge_page(h));
- i_mmap_unlock_write(mapping);
- }
+ VM_BUG_ON(page_mapped(page));
lock_page(page);
/*
@@ -470,7 +451,6 @@ static void remove_inode_hugepages(struc
}
unlock_page(page);
- mutex_unlock(&hugetlb_fault_mutex_table[hash]);
}
huge_pagevec_release(&pvec);
cond_resched();
@@ -624,7 +604,11 @@ static long hugetlbfs_fallocate(struct f
/* addr is the offset within the file (zero based) */
addr = index * hpage_size;
- /* mutex taken here, fault path and hole punch */
+ /*
+ * fault mutex taken here, protects against fault path
+ * and hole punch. inode_lock previously taken protects
+ * against truncation.
+ */
hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping,
index, addr);
mutex_lock(&hugetlb_fault_mutex_table[hash]);
--- a/mm/hugetlb.c~hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization
+++ a/mm/hugetlb.c
@@ -3760,16 +3760,16 @@ static vm_fault_t hugetlb_no_page(struct
}
/*
- * Use page lock to guard against racing truncation
- * before we get page_table_lock.
+ * We can not race with truncation due to holding i_mmap_rwsem.
+ * Check once here for faults beyond end of file.
*/
+ size = i_size_read(mapping->host) >> huge_page_shift(h);
+ if (idx >= size)
+ goto out;
+
retry:
page = find_lock_page(mapping, idx);
if (!page) {
- size = i_size_read(mapping->host) >> huge_page_shift(h);
- if (idx >= size)
- goto out;
-
/*
* Check for page in userfault range
*/
@@ -3859,9 +3859,6 @@ retry:
}
ptl = huge_pte_lock(h, mm, ptep);
- size = i_size_read(mapping->host) >> huge_page_shift(h);
- if (idx >= size)
- goto backout;
ret = 0;
if (!huge_pte_none(huge_ptep_get(ptep)))
@@ -3964,8 +3961,10 @@ vm_fault_t hugetlb_fault(struct mm_struc
/*
* Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
- * until finished with ptep. This prevents huge_pmd_unshare from
- * being called elsewhere and making the ptep no longer valid.
+ * until finished with ptep. This serves two purposes:
+ * 1) It prevents huge_pmd_unshare from being called elsewhere
+ * and making the ptep no longer valid.
+ * 2) It synchronizes us with file truncation.
*
* ptep could have already be assigned via huge_pte_offset. That
* is OK, as huge_pte_alloc will return the same value unless
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
hugetlbfs-use-i_mmap_rwsem-for-more-pmd-sharing-synchronization.patch
hugetlbfs-use-i_mmap_rwsem-to-fix-page-fault-truncate-race.patch
hugetlbfs-remove-unnecessary-code-after-i_mmap_rwsem-synchronization.patch
