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authorHugh Dickins2021-09-02 14:54:21 -0700
committerLinus Torvalds2021-09-03 09:58:11 -0700
commitd144bf6205342a4b5fed5d204ae18849a4de741b (patch)
tree3e015dccb761d5958ba455c8ef4ab796b88aa9d9 /mm/shmem.c
parent050dcb5c85bb47f8151175ca5833aa882cc7fe0c (diff)
huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE
A successful shmem_fallocate() guarantees that the extent has been reserved, even beyond i_size when the FALLOC_FL_KEEP_SIZE flag was used. But that guarantee is broken by shmem_unused_huge_shrink()'s attempts to split huge pages and free their excess beyond i_size; and by other uses of split_huge_page() near i_size. It's sad to add a shmem inode field just for this, but I did not find a better way to keep the guarantee. A flag to say KEEP_SIZE has been used would be cheaper, but I'm averse to unclearable flags. The fallocend field is not perfect either (many disjoint ranges might be fallocated), but good enough; and gains another use later on. Link: https://lkml.kernel.org/r/ca9a146-3a59-6cd3-7f28-e9a044bb1052@google.com Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Yang Shi <shy828301@gmail.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Rik van Riel <riel@surriel.com> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r--mm/shmem.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 9ef579f6cab3..e391325dfc21 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -902,6 +902,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
if (lend == -1)
end = -1; /* unsigned, so actually very big */
+ if (info->fallocend > start && info->fallocend <= end && !unfalloc)
+ info->fallocend = start;
+
pagevec_init(&pvec);
index = start;
while (index < end && find_lock_entries(mapping, index, end - 1,
@@ -2650,7 +2653,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_falloc shmem_falloc;
- pgoff_t start, index, end;
+ pgoff_t start, index, end, undo_fallocend;
int error;
if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -2719,6 +2722,15 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
inode->i_private = &shmem_falloc;
spin_unlock(&inode->i_lock);
+ /*
+ * info->fallocend is only relevant when huge pages might be
+ * involved: to prevent split_huge_page() freeing fallocated
+ * pages when FALLOC_FL_KEEP_SIZE committed beyond i_size.
+ */
+ undo_fallocend = info->fallocend;
+ if (info->fallocend < end)
+ info->fallocend = end;
+
for (index = start; index < end; ) {
struct page *page;
@@ -2733,6 +2745,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
else
error = shmem_getpage(inode, index, &page, SGP_FALLOC);
if (error) {
+ info->fallocend = undo_fallocend;
/* Remove the !PageUptodate pages we added */
if (index > start) {
shmem_undo_range(inode,