On Tue, 10 Nov 2015, Mike Kravetz wrote: > Hugh Dickins pointed out problems with the new hugetlbfs fallocate > hole punch code. These problems are in the routine remove_inode_hugepages > and mostly occur in the case where there are holes in the range of > pages to be removed. These holes could be the result of a previous hole > punch or simply sparse allocation. The current code could access pages > outside the specified range. > > remove_inode_hugepages handles both hole punch and truncate operations. > Page index handling was fixed/cleaned up so that the loop index always > matches the page being processed. The code now only makes a single pass > through the range of pages as it was determined page faults could not > race with truncate. A cond_resched() was added after removing up to > PAGEVEC_SIZE pages. > > Some totally unnecessary code in hugetlbfs_fallocate() that remained from > early development was also removed. > > V3: > Add more descriptive comments and minor improvements as suggested by > Naoya Horiguchi > v2: > Make remove_inode_hugepages simpler after verifying truncate can not > race with page faults here. > > Tested with fallocate tests submitted here: > http://librelist.com/browser//libhugetlbfs/2015/6/25/patch-tests-add-tests-for-fallocate-system-call/ > And, some ftruncate tests under development > > Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages") > Cc: stable@xxxxxxxxxxxxxxx [4.3] > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> > --- > fs/hugetlbfs/inode.c | 65 ++++++++++++++++++++++++++-------------------------- > 1 file changed, 32 insertions(+), 33 deletions(-) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index 316adb9..de4bdfa 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -332,12 +332,17 @@ static void remove_huge_page(struct page *page) > * 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. > + * 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. > */ > @@ -361,46 +366,37 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, > next = start; > while (next < end) { > /* > - * Make sure to never grab more pages that we > - * might possibly need. > + * Don't grab more pages than the number left in the range. > */ > if (end - next < lookup_nr) > lookup_nr = end - next; > > /* > - * This pagevec_lookup() may return pages past 'end', > - * so we must check for page->index > end. > + * When no more pages are found, we are done. > */ > - if (!pagevec_lookup(&pvec, mapping, next, lookup_nr)) { > - if (next == start) > - break; > - next = start; > - continue; > - } > + if (!pagevec_lookup(&pvec, mapping, next, lookup_nr)) > + break; > > for (i = 0; i < pagevec_count(&pvec); ++i) { > struct page *page = pvec.pages[i]; > u32 hash; > > + /* > + * The page (index) could be beyond end. This is > + * only possible in the punch hole case as end is > + * max page offset in the truncate case. > + */ > + next = page->index; > + if (next >= end) > + break; > + > hash = hugetlb_fault_mutex_hash(h, current->mm, > &pseudo_vma, > mapping, next, 0); > mutex_lock(&hugetlb_fault_mutex_table[hash]); > > lock_page(page); > - if (page->index >= end) { > - unlock_page(page); > - mutex_unlock(&hugetlb_fault_mutex_table[hash]); > - next = end; /* we are done */ > - break; > - } > - > - /* > - * If page is mapped, it was faulted in after being > - * unmapped. Do nothing in this race case. In the > - * normal case page is not mapped. > - */ > - if (!page_mapped(page)) { > + if (likely(!page_mapped(page))) { > bool rsv_on_error = !PagePrivate(page); > /* > * We must free the huge page and remove > @@ -421,17 +417,23 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, > hugetlb_fix_reserve_counts( > inode, rsv_on_error); > } > + } else { > + /* > + * If page is mapped, it was faulted in after > + * being unmapped. It indicates a race between > + * hole punch and page fault. Do nothing in > + * this case. Getting here in a truncate > + * operation is a bug. > + */ > + BUG_ON(truncate_op); > } > > - if (page->index > next) > - next = page->index; > - > - ++next; > unlock_page(page); > - > mutex_unlock(&hugetlb_fault_mutex_table[hash]); > } > + ++next; > huge_pagevec_release(&pvec); > + cond_resched(); > } > > if (truncate_op) > @@ -647,9 +649,6 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset, > if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) > i_size_write(inode, offset + len); > inode->i_ctime = CURRENT_TIME; > - spin_lock(&inode->i_lock); > - inode->i_private = NULL; > - spin_unlock(&inode->i_lock); > out: > mutex_unlock(&inode->i_mutex); > return error; > -- > 2.4.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>