On 15.10.25 20:58, Lisa Wang wrote:
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 truncat_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 within guest_memfd memory 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.
Generalize the comment: MF_DELAYED means memory failure was handled and some other part of memory failure will be handled later (e.g. a next access will result in the process being killed). Specifically for guest_memfd, a next access by the guest will result in an error returned to the userspace VMM.
With delayed handling, the filemap continues to hold refcounts on the folio. Hence, take that into account when checking for extra refcounts in me_pagecache_clean(). This is aligned with the implementation in me_swapcache_dirty(), where, if a folio is still in the swap cache, extra_pins is set to true.
Signed-off-by: Lisa Wang wyihan@google.com
mm/memory-failure.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c index df6ee59527dd..77f665c16a73 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -922,9 +922,11 @@ static int kill_accessing_process(struct task_struct *p, unsigned long pfn,
- by the m-f() handler immediately.
- MF_DELAYED - The m-f() handler marks the page as PG_hwpoisoned'ed.
- The page is unmapped, and is removed from the LRU or file mapping.
- An attempt to access the page again will trigger page fault and the
- PF handler will kill the process.
- It means memory_failure was handled (e.g. removed from file mapping or the
- LRU) and some other part of memory failure will be handled later (e.g. a
- next access will result in the process being killed). Specifically for
- guest_memfd, a next access by the guest will result in an error returned to
- the userspace VMM.
- MF_RECOVERED - The m-f() handler marks the page as PG_hwpoisoned'ed.
- The page has been completely isolated, that is, unmapped, taken out of
@@ -999,6 +1001,9 @@ 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 == MF_DELAYED)return err;- if (err != 0) pr_info("%#lx: Failed to punch page: %d\n", pfn, err); else if (!filemap_release_folio(folio, GFP_NOIO))
@@ -1108,18 +1113,19 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p) goto out; }
- /*
* The shmem page is kept in page cache instead of truncating* so is expected to have an extra refcount after error-handling.*/- extra_pins = shmem_mapping(mapping);
- /*
*/ ret = truncate_error_folio(folio, page_to_pfn(p), mapping);
- Truncation is a bit tricky. Enable it per file system for now.
- Open: to take i_rwsem or not for this? Right now we don't.
- /*
* The shmem page, or any page with MF_DELAYED error handling, is kept in* page cache instead of truncating, so is expected to have an extra* refcount after error-handling.*/- extra_pins = shmem_mapping(mapping) || ret == MF_DELAYED;
Well, to do it cleanly shouldn't we let shmem_error_remove_folio() also return MF_DELAYED and remove this shmem special case?
Or is there a good reason shmem_mapping() wants to return 0 -- and maybe guest_memfd would also wan to do that?
Just reading the code here the inconsistency is unclear.