[PATCH] mm: fix cpu hangs on truncating last page of a 16t sparse file

[angelo]

Hi all,

running xfstests, generic 308 on whatever 32bit arch is possible
to observe cpu to hang near 100% on unlink.
The test removes a sparse file of length 16tera where only the last
4096 bytes block is mapped.
At line 265 of truncate.c there is a
if (index >= end)
    break;
But if index is, as in this case, a 4294967295, it match -1 used as
eof. Hence the cpu loops 100% just after.

-------------------

On 32bit archs, with CONFIG_LBDAF=y, if truncating last page
of a 16tera file, "index" variable is set to 4294967295, and hence
matches with -1 used as EOF value. This result in an inifite loop
when unlink is executed on this file.

Signed-off-by: Angelo Dureghello <angelo@xxxxxxxx>
---
 mm/truncate.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index 76e35ad..3751034 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -283,14 +283,15 @@ void truncate_inode_pages_range(struct 
address_space *mapping,
                pagevec_remove_exceptionals(&pvec);
                pagevec_release(&pvec);
                cond_resched();
-               index++;
+               if (index < end)
+                       index++;
        }

        if (partial_start) {
                struct page *page = find_lock_page(mapping, start - 1);
                if (page) {
                        unsigned int top = PAGE_CACHE_SIZE;
-                       if (start > end) {
+                       if (start > end && end != -1) {
                                /* Truncation within a single page */
                                top = partial_end;
                                partial_end = 0;
@@ -322,7 +323,7 @@ void truncate_inode_pages_range(struct address_space 
*mapping,
         * If the truncation happened within a single page no pages
         * will be released, just zeroed, so we can bail out now.
         */
-       if (start >= end)
+       if (start >= end && end != -1)
                return;

        index = start;
@@ -337,7 +338,7 @@ void truncate_inode_pages_range(struct address_space 
*mapping,
                        index = start;
                        continue;
                }
-               if (index == start && indices[0] >= end) {
+               if (index == start && (indices[0] >= end && end != -1)) {
                        /* All gone out of hole to be punched, we're 
done */
                        pagevec_remove_exceptionals(&pvec);
                        pagevec_release(&pvec);
@@ -348,7 +349,7 @@ void truncate_inode_pages_range(struct address_space 
*mapping,

                        /* We rely upon deletion not changing 
page->index */
                        index = indices[i];
-                       if (index >= end) {
+                       if (index >= end && (end != -1)) {
                                /* Restart punch to make sure all gone */
                                index = start - 1;
                                break;
--
2.5.3









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