From: Charan Teja Reddy <charante@codeaurora.org>
To: akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz,
david@redhat.com, rientjes@google.com, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, vinmenon@codeaurora.org,
Charan Teja Reddy <charante@codeaurora.org>
Subject: [PATCH V2] mm, page_alloc: fix core hung in free_pcppages_bulk()
Date: Tue, 11 Aug 2020 18:28:23 +0530 [thread overview]
Message-ID: <1597150703-19003-1-git-send-email-charante@codeaurora.org> (raw)
The following race is observed with the repeated online, offline and a
delay between two successive online of memory blocks of movable zone.
P1 P2
Online the first memory block in
the movable zone. The pcp struct
values are initialized to default
values,i.e., pcp->high = 0 &
pcp->batch = 1.
Allocate the pages from the
movable zone.
Try to Online the second memory
block in the movable zone thus it
entered the online_pages() but yet
to call zone_pcp_update().
This process is entered into
the exit path thus it tries
to release the order-0 pages
to pcp lists through
free_unref_page_commit().
As pcp->high = 0, pcp->count = 1
proceed to call the function
free_pcppages_bulk().
Update the pcp values thus the
new pcp values are like, say,
pcp->high = 378, pcp->batch = 63.
Read the pcp's batch value using
READ_ONCE() and pass the same to
free_pcppages_bulk(), pcp values
passed here are, batch = 63,
count = 1.
Since num of pages in the pcp
lists are less than ->batch,
then it will stuck in
while(list_empty(list)) loop
with interrupts disabled thus
a core hung.
Avoid this by ensuring free_pcppages_bulk() is called with proper count
of pcp list pages.
The mentioned race is some what easily reproducible without [1] because
pcp's are not updated for the first memory block online and thus there
is a enough race window for P2 between alloc+free and pcp struct values
update through onlining of second memory block.
With [1], the race is still exists but it is very much narrow as we
update the pcp struct values for the first memory block online itself.
[1]: https://patchwork.kernel.org/patch/11696389/
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
---
v1: https://patchwork.kernel.org/patch/11707637/
mm/page_alloc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e4896e6..839039f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1304,6 +1304,11 @@ static void free_pcppages_bulk(struct zone *zone, int count,
struct page *page, *tmp;
LIST_HEAD(head);
+ /*
+ * Ensure proper count is passed which otherwise would stuck in the
+ * below while (list_empty(list)) loop.
+ */
+ count = min(pcp->count, count);
while (count) {
struct list_head *list;
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
next reply other threads:[~2020-08-11 12:58 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-11 12:58 Charan Teja Reddy [this message]
2020-08-11 21:05 ` [PATCH V2] mm, page_alloc: fix core hung in free_pcppages_bulk() David Hildenbrand
2020-08-12 9:46 ` Charan Teja Kalla
2020-08-12 10:00 ` David Hildenbrand
2020-08-12 10:11 ` Charan Teja Kalla
2020-08-13 9:32 ` David Hildenbrand
2020-08-12 18:53 ` David Rientjes
2020-08-13 11:41 ` Michal Hocko
2020-08-13 16:21 ` Charan Teja Kalla
2020-08-13 16:30 ` Michal Hocko
2020-08-13 17:27 ` Charan Teja Kalla
2020-08-14 6:39 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1597150703-19003-1-git-send-email-charante@codeaurora.org \
--to=charante@codeaurora.org \
--cc=akpm@linux-foundation.org \
--cc=david@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=rientjes@google.com \
--cc=vbabka@suse.cz \
--cc=vinmenon@codeaurora.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).