[PATCH mm-hotfixes] shmem: minor fixes to splice-read implementation

[Hugh Dickins <hughd@google.com>]

HWPoison: my reading of folio_test_hwpoison() is that it only tests the
head page of a large folio, whereas splice_folio_into_pipe() will splice
as much of the folio as it can: so for safety we should also check the
has_hwpoisoned flag, set if any of the folio's pages are hwpoisoned.
(Perhaps that ugliness can be improved at the mm end later.)

The call to splice_zeropage_into_pipe() risked overrunning past EOF:
ask it for "part" not "len".

Fixes: bd194b187115 ("shmem: Implement splice-read")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: David Howells <dhowells@redhat.com>
---
This went into Jens's tree for a while, but got lost when another version
of the splice series arrived.  The reviewed version did contain two more
mods: but its !len check is now done at the upper level, and its *ppos
check is unnecessary, given the *ppos check at the start of the loop.

 mm/shmem.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 2f2e0e618072..f5af4b943e42 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2796,7 +2796,8 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
 		if (*ppos >= i_size_read(inode))
 			break;
 
-		error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio, SGP_READ);
+		error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio,
+					SGP_READ);
 		if (error) {
 			if (error == -EINVAL)
 				error = 0;
@@ -2805,7 +2806,9 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
 		if (folio) {
 			folio_unlock(folio);
 
-			if (folio_test_hwpoison(folio)) {
+			if (folio_test_hwpoison(folio) ||
+			    (folio_test_large(folio) &&
+			     folio_test_has_hwpoisoned(folio))) {
 				error = -EIO;
 				break;
 			}
@@ -2841,7 +2844,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
 			folio_put(folio);
 			folio = NULL;
 		} else {
-			n = splice_zeropage_into_pipe(pipe, *ppos, len);
+			n = splice_zeropage_into_pipe(pipe, *ppos, part);
 		}
 
 		if (!n)
-- 
2.35.3