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hugetlbfs: revert "Use i_mmap_rwsem to fix page fault/truncate race" 

This reverts c86aa7bbfd

The reverted commit caused ABBA deadlocks when file migration raced with
file eviction for specific hugetlbfs files.  This was discovered with a
modified version of the LTP move_pages12 test.

The purpose of the reverted patch was to close a long existing race
between hugetlbfs file truncation and page faults.  After more analysis
of the patch and impacted code, it was determined that i_mmap_rwsem can
not be used for all required synchronization.  Therefore, revert this
patch while working an another approach to the underlying issue.

Link: http://lkml.kernel.org/r/20190103235452.29335-1-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: Jan Stancek <jstancek@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Kravetz 2019-01-08 15:23:32 -08:00 committed by Linus Torvalds
parent 8ab88c7169
commit e7c5809779
2 changed files with 44 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
fs/hugetlbfs/inode.c
View File

@ -383,16 +383,17 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end)
* 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.
* 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.
* 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.
*
* Callers of this routine must hold the i_mmap_rwsem in write mode to prevent
* races with page faults.
*
* pages are not modified. Page faults can race with hole punch.
* This is indicated if we find a mapped page.
* 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.
*/
@ -422,14 +423,32 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
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]);
/*
* A mapped page is impossible as callers should unmap
* all references before calling. And, i_mmap_rwsem
* prevents the creation of additional mappings.
* 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.
*/
VM_BUG_ON(page_mapped(page));
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);
}
lock_page(page);
/*
@ -451,6 +470,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
}
unlock_page(page);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
}
huge_pagevec_release(&pvec);
cond_resched();
@ -462,20 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
static void hugetlbfs_evict_inode(struct inode *inode)
{
struct address_space *mapping = inode->i_mapping;
struct resv_map *resv_map;
/*
* The vfs layer guarantees that there are no other users of this
* inode. Therefore, it would be safe to call remove_inode_hugepages
* without holding i_mmap_rwsem. We acquire and hold here to be
* consistent with other callers. Since there will be no contention
* on the semaphore, overhead is negligible.
*/
i_mmap_lock_write(mapping);
remove_inode_hugepages(inode, 0, LLONG_MAX);
i_mmap_unlock_write(mapping);
resv_map = (struct resv_map *)inode->i_mapping->private_data;
/* root inode doesn't have the resv_map, so we should check it */
if (resv_map)
@ -496,8 +505,8 @@ static int hugetlb_vmtruncate(struct inode *inode, loff_t offset)
i_mmap_lock_write(mapping);
if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0);
remove_inode_hugepages(inode, offset, LLONG_MAX);
i_mmap_unlock_write(mapping);
remove_inode_hugepages(inode, offset, LLONG_MAX);
return 0;
}
@ -531,8 +540,8 @@ static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
hugetlb_vmdelete_list(&mapping->i_mmap,
hole_start >> PAGE_SHIFT,
hole_end >> PAGE_SHIFT);
remove_inode_hugepages(inode, hole_start, hole_end);
i_mmap_unlock_write(mapping);
remove_inode_hugepages(inode, hole_start, hole_end);
inode_unlock(inode);
}
@ -615,11 +624,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
/* addr is the offset within the file (zero based) */
addr = index * hpage_size;
/*
* fault mutex taken here, protects against fault path
* and hole punch. inode_lock previously taken protects
* against truncation.
*/
/* mutex taken here, fault path and hole punch */
hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping,
index, addr);
mutex_lock(&hugetlb_fault_mutex_table[hash]);

21
mm/hugetlb.c
View File

@ -3755,16 +3755,16 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
}
/*
* We can not race with truncation due to holding i_mmap_rwsem.
* Check once here for faults beyond end of file.
* Use page lock to guard against racing truncation
* before we get page_table_lock.
*/
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
*/
@ -3854,6 +3854,9 @@ 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)))
@ -3956,10 +3959,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
/*
* Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
* 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.
* until finished with ptep. This prevents huge_pmd_unshare from
* being called elsewhere and making the ptep no longer valid.
*
* ptep could have already be assigned via huge_pte_offset. That
* is OK, as huge_pte_alloc will return the same value unless