[PATCH 6.0 060/157] tmpfs: fix data loss from failed fallocate

Greg Kroah-Hartman
2022-12-12T13:40:26Z

From: Hugh Dickins <hughd@google.com>

commit 44bcabd70cf1425b4243e02251c02b01638a8287 upstream.

Fix tmpfs data loss when the fallocate system call is interrupted by a
signal, or fails for some other reason. The partial folio handling in
shmem_undo_range() forgot to consider this unfalloc case, and was liable
to erase or truncate out data which had already been committed earlier.

It turns out that none of the partial folio handling there is appropriate
for the unfalloc case, which just wants to proceed to removal of whole
folios: which find_get_entries() provides, even when partially covered.

Original patch by Rui Wang.

Link: https://lore.kernel.org/linux-mm/33b85d82.7764.1842e9ab207.Coremail.chenguoqic@163.com/
Link: https://lkml.kernel.org/r/a5dac112-cf4b-7af-a33-f386e347fd38@google.com
Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Guoqi Chen <chenguoqic@163.com>
Link: https://lore.kernel.org/all/20221101032248.819360-1-kernel@hev.cc/
Cc: Rui Wang <kernel@hev.cc>
Cc: Huacai Chen <chenhuacai@loongson.cn>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: <stable@vger.kernel.org> [5.17+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/shmem.c | 11 +++++++++++
1 file changed, 11 insertions(+)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -958,6 +958,15 @@ static void shmem_undo_range(struct inod
index++;
}

+ /*
+ * When undoing a failed fallocate, we want none of the partial folio
+ * zeroing and splitting below, but shall want to truncate the whole
+ * folio when !uptodate indicates that it was added by this fallocate,
+ * even when [lstart, lend] covers only a part of the folio.
+ */
+ if (unfalloc)
+ goto whole_folios;
+
same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
if (folio) {
@@ -983,6 +992,8 @@ static void shmem_undo_range(struct inod
folio_put(folio);
}

+whole_folios:
+
index = start;
while (index < end) {
cond_resched();