FAILED: patch "[PATCH] Multi-gen LRU: avoid race in inc_min_seq()" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x bb5e7f234eacf34b65be67ebb3613e3b8cf11b87
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023091354-atom-tinderbox-b9be@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

bb5e7f234eac ("Multi-gen LRU: avoid race in inc_min_seq()") 391655fe08d1 ("mm: multi-gen LRU: rename lru_gen_struct to lru_gen_folio")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bb5e7f234eacf34b65be67ebb3613e3b8cf11b87 Mon Sep 17 00:00:00 2001
From: Kalesh Singh <[email protected]>
Date: Tue, 1 Aug 2023 19:56:03 -0700
Subject: [PATCH] Multi-gen LRU: avoid race in inc_min_seq()

inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This is because the generations are reused (the last oldest now empty generation will become the next youngest generation).

inc_min_seq() is retried until successful, dropping the lru_lock and yielding the CPU on each failure, and retaking the lock before trying again:

        while (!inc_min_seq(lruvec, type, can_swap)) {
                spin_unlock_irq(&lruvec->lru_lock);
                cond_resched();
                spin_lock_irq(&lruvec->lru_lock);
        }

However, the initial condition that required incrementing the min_seq (nr_gens == MAX_NR_GENS) is not retested. This can change by another call to inc_max_seq() from run_aging() with force_scan=true from the debugfs interface.

Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid unnecessarily incrementing the min_seq by rechecking the number of generations before each attempt.

This issue was uncovered in previous discussion on the list by Yu Zhao and Aneesh Kumar [1].

[1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_dpf+zR3w@mail.gmail.com/

index 489a4fc7d9b1..6eecd291756c 100644
@@ -4439,7 +4439,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
 	int prev, next;
 	int type, zone;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
-
+restart:
 	spin_lock_irq(&lruvec->lru_lock);
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));

@@ -4450,11 +4450,12 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
 
 		VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap));
 
-		while (!inc_min_seq(lruvec, type, can_swap)) {
-			spin_unlock_irq(&lruvec->lru_lock);
-			cond_resched();
-			spin_lock_irq(&lruvec->lru_lock);
-		}
+		if (inc_min_seq(lruvec, type, can_swap))
+			continue;
+
+		spin_unlock_irq(&lruvec->lru_lock);
+		cond_resched();
+		goto restart;
 	}
 
 	/*

inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This is because the generations are reused (the last oldest now empty generation will become the next youngest generation).

inc_min_seq() is retried until successful, dropping the lru_lock and yielding the CPU on each failure, and retaking the lock before trying again:

        while (!inc_min_seq(lruvec, type, can_swap)) {
                spin_unlock_irq(&lruvec->lru_lock);
                cond_resched();
                spin_lock_irq(&lruvec->lru_lock);
        }

However, the initial condition that required incrementing the min_seq (nr_gens == MAX_NR_GENS) is not retested. This can change by another call to inc_max_seq() from run_aging() with force_scan=true from the debugfs interface.

Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid unnecessarily incrementing the min_seq by rechecking the number of generations before each attempt.

This issue was uncovered in previous discussion on the list by Yu Zhao and Aneesh Kumar [1].

[1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_dpf+zR3w@mail.gmail.com/

---
 mm/vmscan.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

index d18296109aa7..251e7b8a0bc0 100644
@@ -4331,6 +4331,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
 	int type, zone;
 	struct lru_gen_struct *lrugen = &lruvec->lrugen;
 
+restart:
 	spin_lock_irq(&lruvec->lru_lock);
 
 	VM_WARN_ON_ONCE(!seq_is_valid(lruvec));

@@ -4341,11 +4342,12 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
 
 		VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap));
 
-		while (!inc_min_seq(lruvec, type, can_swap)) {
-			spin_unlock_irq(&lruvec->lru_lock);
-			cond_resched();
-			spin_lock_irq(&lruvec->lru_lock);
-		}
+		if (inc_min_seq(lruvec, type, can_swap))
+			continue;
+
+		spin_unlock_irq(&lruvec->lru_lock);
+		cond_resched();
+		goto restart;
 	}
 
 	/*

2.42.0.283.g2d96d420d3-goog

Now queued up, thanks.

greg k-h