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mm/swapfile: fix list iteration when next node is removed during discard 

Patch series "mm/swapfile: fix and cleanup swap list iterations", v2.

This series fixes a potential list iteration issue in swap_sync_discard()
when devices are removed, and includes a cleanup for
__folio_throttle_swaprate().


This patch (of 2):

When the next node is removed from the plist (e.g.  by swapoff),
plist_del() makes the node point to itself, causing the iteration to loop
on the same entry indefinitely.

Add a plist_node_empty() check to detect this case and restart iteration,
allowing swap_sync_discard() to continue processing remaining swap devices
that still have pending discard entries.

Additionally, switch from swap_avail_lock/swap_avail_head to
swap_lock/swap_active_head so that iteration is only affected by swapoff
operations rather than frequent availability changes, reducing exceptional
condition checks and lock contention.

Link: https://lkml.kernel.org/r/20251127100303.783198-1-youngjun.park@lge.com
Link: https://lkml.kernel.org/r/20251127100303.783198-2-youngjun.park@lge.com
Fixes: 686ea517f471 ("mm, swap: do not perform synchronous discard during allocation")
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
Suggested-by: Kairui Song <kasong@tencent.com>
Acked-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
pull/1354/merge
Youngjun Park 2025-11-27 19:03:02 +09:00 committed by Andrew Morton
parent 12f0cd3933
commit f9e82f99b3
1 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
mm/swapfile.c
View File

@ -1387,9 +1387,10 @@ static bool swap_sync_discard(void)
bool ret = false;
struct swap_info_struct *si, *next;
spin_lock(&swap_avail_lock);
plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
spin_unlock(&swap_avail_lock);
spin_lock(&swap_lock);
start_over:
plist_for_each_entry_safe(si, next, &swap_active_head, list) {
spin_unlock(&swap_lock);
if (get_swap_device_info(si)) {
if (si->flags & SWP_PAGE_DISCARD)
ret = swap_do_scheduled_discard(si);
@ -1397,9 +1398,12 @@ static bool swap_sync_discard(void)
}
if (ret)
return true;
spin_lock(&swap_avail_lock);
spin_lock(&swap_lock);
if (plist_node_empty(&next->list))
goto start_over;
}
spin_unlock(&swap_avail_lock);
spin_unlock(&swap_lock);
return false;
}