[PATCH v5 2/5] mm: memory_failure: Allow truncate_error_folio to return MF_DELAYED

The .error_remove_folio a_ops is used by different filesystems to handle
folio truncation upon discovery of a memory failure in the memory
associated with the given folio.

Currently, MF_DELAYED is treated as an error, causing "Failed to punch
page" to be written to the console. MF_DELAYED is then relayed to the
caller of truncate_error_folio() as MF_FAILED. This further causes
memory_failure() to return -EBUSY, which then always causes a SIGBUS.

This is also implies that regardless of whether the thread's memory
corruption kill policy is PR_MCE_KILL_EARLY or PR_MCE_KILL_LATE, a
memory failure with MF_DELAYED will always cause a SIGBUS.

Update truncate_error_folio() to return MF_DELAYED to the caller if the
.error_remove_folio() callback reports MF_DELAYED.

Acked-by: David Hildenbrand (Arm) <[email protected]>
Acked-by: Miaohe Lin <[email protected]>
Reviewed-by: Ackerley Tng <[email protected]>
Fixes: 6a46079cf57a ("HWPOISON: The high level memory error handler in the VM v7")
Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
Signed-off-by: Lisa Wang <[email protected]>
---
 mm/memory-failure.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e698d0e9711d..37ea23489b75 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -939,10 +939,12 @@ static int truncate_error_folio(struct folio *folio, unsigned long pfn,
 	if (mapping->a_ops->error_remove_folio) {
 		int err = mapping->a_ops->error_remove_folio(mapping, folio);
 
-		if (err != 0)
+		if (err == MF_DELAYED)
+			ret = err;
+		else if (err != 0)
 			pr_info("%#lx: Failed to punch page: %d\n", pfn, err);
 		else if (!filemap_release_folio(folio, GFP_NOIO))
-			pr_info("%#lx: failed to release buffers\n", pfn);
+			pr_info("%#lx: Failed to release buffers\n", pfn);
 		else
 			ret = MF_RECOVERED;
 	} else {

-- 
2.55.0.766.g2966f0265a-goog