On 5/9/2024 1:30 AM, Miaohe Lin wrote:
On 2024/5/9 1:45, Jane Chu wrote:
On 5/8/2024 1:08 AM, Miaohe Lin wrote:
On 2024/5/7 4:26, Jane Chu wrote:
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.
In try_to_split_thp_page(), if split_huge_page fails, i.e. ret != 0, put_page() is called. See below:
static int try_to_split_thp_page(struct page *page)
{
int ret;
lock_page(page);
ret = split_huge_page(page);
unlock_page(page);
if (unlikely(ret))
put_page(page);
^^^^^^^^^^^^^^^^^^^^^^^
return ret;
}
Or am I miss something?
I think you caught a bug in my code, thanks!
How about moving put_page() outside try_to_split_thp_page() ?
If you want to send SIGBUS in the event of thp split fail, it might be required to do so.
I think kill_procs_now() needs extra thp refcnt to do its work.
Agreed. I added an boolean to try_to_split_thp_page(),the boolean
indicates whether to put_page().
In case of kill_procs_now(), put_page() is called afterwards.
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) {
Only in MF_ACTION_REQUIRED case, SIGBUS is sent to processes when thp split failed. Any reson under it?
I took a clue from kill_accessing_process() which is invoked only if MF_ACTION_REQUIRED is set.
The usual code path for delivery signal is
if page-is-dirty or MF_MUST_KILL-is-set or umap-failed, then
- send SIGKILL if vaddr is -EFAULT
- send SIGBUS with BUS_MCEERR_AR if MF_ACTION_REQUIRED is set
- send SIGBUS with BUS_MCEERR_AO if MF_ACTION_REQUIRED is not set and process elected for MCE-early-kill
So, if kill_procs_now() is invoked only if MF_ACTION_REQUIRED (as it is in the patch), one can argue that
the MCE-early-kill request is not honored which deviates from the existing behavior.
Perhaps I should remove the
+ if (flags & MF_ACTION_REQUIRED) {
I tend to agree MCE-early-kill request should be honored when try to kill process.
Thanks.
.
Thanks,
-jane
