* [PATCH] mm/madvise: elevate page refcount while isolating in process_madvise()
@ 2021-12-15 12:23 Charan Teja Reddy
2021-12-15 13:55 ` Matthew Wilcox
0 siblings, 1 reply; 3+ messages in thread
From: Charan Teja Reddy @ 2021-12-15 12:23 UTC (permalink / raw)
To: akpm, minchan, surenb, vbabka, rientjes
Cc: linux-mm, linux-kernel, Charan Teja Reddy
The documentation of isolate_lru_page() says that, "it must be called
with an elevated refcount on the page", which is not followed while
isolating pages in process_madvise() system call with advise
MADV_PAGEOUT. Fix it.
Signed-off-by: Charan Teja Reddy <quic_charante@quicinc.com>
---
mm/madvise.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index 0734db8..4c4a8e9 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -317,6 +317,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
pte_t *orig_pte, *pte, ptent;
spinlock_t *ptl;
struct page *page = NULL;
+ int ret;
LIST_HEAD(page_list);
if (fatal_signal_pending(current))
@@ -373,12 +374,15 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
ClearPageReferenced(page);
test_and_clear_page_young(page);
if (pageout) {
- if (!isolate_lru_page(page)) {
+ get_page(page);
+ ret = isolate_lru_page(page);
+ if (!ret) {
if (PageUnevictable(page))
putback_lru_page(page);
else
list_add(&page->lru, &page_list);
}
+ put_page(page);
} else
deactivate_page(page);
huge_unlock:
@@ -459,12 +463,15 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
ClearPageReferenced(page);
test_and_clear_page_young(page);
if (pageout) {
- if (!isolate_lru_page(page)) {
+ get_page(page);
+ ret = isolate_lru_page(page);
+ if (!ret) {
if (PageUnevictable(page))
putback_lru_page(page);
else
list_add(&page->lru, &page_list);
}
+ put_page(page);
} else
deactivate_page(page);
}
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/madvise: elevate page refcount while isolating in process_madvise()
2021-12-15 12:23 [PATCH] mm/madvise: elevate page refcount while isolating in process_madvise() Charan Teja Reddy
@ 2021-12-15 13:55 ` Matthew Wilcox
2021-12-15 15:39 ` Charan Teja Kalla
0 siblings, 1 reply; 3+ messages in thread
From: Matthew Wilcox @ 2021-12-15 13:55 UTC (permalink / raw)
To: Charan Teja Reddy
Cc: akpm, minchan, surenb, vbabka, rientjes, linux-mm, linux-kernel
On Wed, Dec 15, 2021 at 05:53:39PM +0530, Charan Teja Reddy wrote:
> The documentation of isolate_lru_page() says that, "it must be called
> with an elevated refcount on the page", which is not followed while
> isolating pages in process_madvise() system call with advise
> MADV_PAGEOUT. Fix it.
We hold the mmap_lock over the call to this function, so the reference
to the page from the page tables cannot go away. There's no need to
grab an extra reference here.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm/madvise: elevate page refcount while isolating in process_madvise()
2021-12-15 13:55 ` Matthew Wilcox
@ 2021-12-15 15:39 ` Charan Teja Kalla
0 siblings, 0 replies; 3+ messages in thread
From: Charan Teja Kalla @ 2021-12-15 15:39 UTC (permalink / raw)
To: Matthew Wilcox
Cc: akpm, minchan, surenb, vbabka, rientjes, linux-mm, linux-kernel
On 12/15/2021 7:25 PM, Matthew Wilcox wrote:
> On Wed, Dec 15, 2021 at 05:53:39PM +0530, Charan Teja Reddy wrote:
>> The documentation of isolate_lru_page() says that, "it must be called
>> with an elevated refcount on the page", which is not followed while
>> isolating pages in process_madvise() system call with advise
>> MADV_PAGEOUT. Fix it.
>
> We hold the mmap_lock over the call to this function, so the reference
> to the page from the page tables cannot go away. There's no need to
> grab an extra reference here.
Thanks Matthew for clearing such fundamentals.
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-12-15 12:23 [PATCH] mm/madvise: elevate page refcount while isolating in process_madvise() Charan Teja Reddy
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