On 5/5/2024 12:00 AM, Miaohe Lin wrote:
On 2024/5/2 7:24, Jane Chu wrote:
When handle hwpoison in a GUP longterm pin'ed thp page,
try_to_split_thp_page() will fail. And at this point, there is little else
the kernel could do except sending a SIGBUS to the user process, thus
give it a chance to recover.
Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
Thanks for your patch. Some comments below.
---
mm/memory-failure.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 7fcf182abb96..67f4d24a98e7 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2168,6 +2168,37 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
return rc;
}
+/*
+ * The calling condition is as such: thp split failed, page might have
+ * been GUP longterm pinned, not much can be done for recovery.
+ * But a SIGBUS should be delivered with vaddr provided so that the user
+ * application has a chance to recover. Also, application processes'
+ * election for MCE early killed will be honored.
+ */
+static int kill_procs_now(struct page *p, unsigned long pfn, int flags,
+ struct page *hpage)
+{
+ struct folio *folio = page_folio(hpage);
+ LIST_HEAD(tokill);
+ int res = -EHWPOISON;
+
+ /* deal with user pages only */
+ if (PageReserved(p) || PageSlab(p) || PageTable(p) || PageOffline(p))
+ res = -EBUSY;
+ if (!(PageLRU(hpage) || PageHuge(p)))
+ res = -EBUSY;
Above checks seems unneeded. We already know it's thp?
Agreed.
I lifted these checks from hwpoison_user_mapping() with a hope to make
kill_procs_now() more generic,
such as, potentially replacing kill_accessing_processes() for
re-accessing hwpoisoned page.
But I backed out at last, due to concerns that my tests might not have
covered sufficient number of scenarios.
+
+ if (res == -EHWPOISON) {
+ collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
+ kill_procs(&tokill, true, pfn, flags);
+ }
+
+ if (flags & MF_COUNT_INCREASED)
+ put_page(p);
This if block is broken. put_page() has been done when try_to_split_thp_page() fails?
put_page() has not been done if try_to_split_thp_page() fails, and I
think it should.
I will revise the code so that put_page() is called regardless
MF_ACTION_REQUIRED is set or not.
+
action_result is missing?
Indeed, action_result() isn't always called, referring to the
re-accessing hwpoison scenarios.
In this case, I think the reason is that, we just killed the process
and there is nothing
else to do or to report.
+ return res;
+}
+
/**
* memory_failure - Handle memory failure of a page.
* @pfn: Page Number of the corrupted page
@@ -2297,6 +2328,11 @@ int memory_failure(unsigned long pfn, int flags)
*/
SetPageHasHWPoisoned(hpage);
if (try_to_split_thp_page(p) < 0) {
Should hwpoison_filter() be called in this case?
Yes, it should. I will add the hwpoison_filter check.
+ if (flags & MF_ACTION_REQUIRED) {
+ pr_err("%#lx: thp split failed\n", pfn);
+ res = kill_procs_now(p, pfn, flags, hpage);
Can we use hwpoison_user_mappings() directly here?
I thought about using hwpoison_user_mappings() with an extra flag, but
gave up in the end.
Because most of the code there are not needed, such as the checks you
mentioned above,
and umapping etc.
thanks!
-jane
Thanks.
.
+ goto unlock_mutex;
+ }
res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
goto unlock_mutex;
}
