From a1cd02b590d75df577e50be044c87125698c4dd2 Mon Sep 17 00:00:00 2001 From: Kalesh Singh Date: Tue, 1 Aug 2023 19:56:03 -0700 Subject: [PATCH] FROMGIT: BACKPORT: 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/ Link: https://lkml.kernel.org/r/20230802025606.346758-2-kaleshsingh@google.com Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface") Change-Id: I89e84ef2927eb1b0091f1be28bd03eb04dee4c57 Signed-off-by: Kalesh Singh Tested-by: AngeloGioacchino Del Regno [mediatek] Tested-by: Charan Teja Kalla Cc: Yu Zhao Cc: Aneesh Kumar K V Cc: Barry Song Cc: Brian Geffon Cc: Jan Alexander Steffens (heftig) Cc: Lecopzer Chen Cc: Matthias Brugger Cc: Oleksandr Natalenko Cc: Qi Zheng Cc: Steven Barrett Cc: Suleiman Souhlal Cc: Suren Baghdasaryan Cc: Signed-off-by: Andrew Morton (cherry picked from commit 250dbd10306126b06415afda8adfc27b2b780428 https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable) Bug: 288383787 Bug: 291719697 [ Fix trivial conflict in inc_max_seq() due to page -> folio Kalesh Singh ] Signed-off-by: Kalesh Singh --- mm/vmscan.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index e5dcd5d00ca5..5055351dae53 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4138,7 +4138,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool full_scan) int prev, next; 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)); @@ -4154,6 +4154,13 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool full_scan) 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; + } /*