The patch titled
Subject: mm-swap-fix-race-when-skipping-swapcache-v4
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-swap-fix-race-when-skipping-swapcache-v4.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-fix-race-when-skipping-swapcache-v4.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Kairui Song <kasong@xxxxxxxxxxx>
Subject: mm-swap-fix-race-when-skipping-swapcache-v4
Date: Mon, 19 Feb 2024 16:20:40 +0800
Add a schedule() if raced to prevent repeated page faults wasting CPU and
add noise to perf statistics.
Use a bool to state the special case instead of reusing existing variables
fixing error handling [Minchan Kim].
Use schedule_timeout_uninterruptible(1) for now instead of schedule() to
prevent the busy faulting task holds CPU and livelocks [Huang, Ying].
Link: https://lkml.kernel.org/r/20240219082040.7495-1-ryncsn@xxxxxxxxx
Fixes: 0bcac06f27d7 ("mm, swap: skip swapcache for swapin of synchronous device")
Link: https://github.com/ryncsn/emm-test-project/tree/master/swap-stress-race [1]
Reported-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Closes: https://lore.kernel.org/lkml/87bk92gqpx.fsf_-_@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Chris Li <chrisl@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Barry Song <21cnbao@xxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
--- a/mm/memory.c~mm-swap-fix-race-when-skipping-swapcache-v4
+++ a/mm/memory.c
@@ -3799,6 +3799,7 @@ vm_fault_t do_swap_page(struct vm_fault
struct page *page;
struct swap_info_struct *si = NULL;
rmap_t rmap_flags = RMAP_NONE;
+ bool need_clear_cache = false;
bool exclusive = false;
swp_entry_t entry;
pte_t pte;
@@ -3874,8 +3875,12 @@ vm_fault_t do_swap_page(struct vm_fault
* reusing the same entry. It's undetectable as
* pte_same() returns true due to entry reuse.
*/
- if (swapcache_prepare(entry))
+ if (swapcache_prepare(entry)) {
+ /* Relax a bit to prevent rapid repeated page faults */
+ schedule_timeout_uninterruptible(1);
goto out;
+ }
+ need_clear_cache = true;
/* skip swapcache */
folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
@@ -4126,10 +4131,10 @@ vm_fault_t do_swap_page(struct vm_fault
unlock:
if (vmf->pte)
pte_unmap_unlock(vmf->pte, vmf->ptl);
+out:
/* Clear the swap cache pin for direct swapin after PTL unlock */
- if (folio && !swapcache)
+ if (need_clear_cache)
swapcache_clear(si, entry);
-out:
if (si)
put_swap_device(si);
return ret;
@@ -4137,8 +4142,6 @@ out_nomap:
if (vmf->pte)
pte_unmap_unlock(vmf->pte, vmf->ptl);
out_page:
- if (!swapcache)
- swapcache_clear(si, entry);
folio_unlock(folio);
out_release:
folio_put(folio);
@@ -4146,6 +4149,8 @@ out_release:
folio_unlock(swapcache);
folio_put(swapcache);
}
+ if (need_clear_cache)
+ swapcache_clear(si, entry);
if (si)
put_swap_device(si);
return ret;
_
Patches currently in -mm which might be from kasong@xxxxxxxxxxx are
mm-swap-fix-race-when-skipping-swapcache.patch
mm-swap-fix-race-when-skipping-swapcache-v4.patch
