xswap_try_shrink() was called directly from __free_cluster() while holding ci->lock. The shrink path calls xswap_unmap_clusters() which unmaps vmalloc pages backing cluster_info, and on return swap_cache_del_folio() tries swap_cluster_unlock(ci) on the now- unmapped address — crashing on a not-present page. Replace direct calls with schedule_work() so shrink runs in an independent workqueue context where no cluster locks are held. Use cancel_work_sync() during swapoff to ensure no pending shrink work races with the VM area teardown. Signed-off-by: Baoquan He --- include/linux/swap.h | 1 + mm/swapfile.c | 19 +++++++++++++------ 2 files changed, 14 insertions(+), 6 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 4f4583f9a4e5..a5b323374769 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -255,6 +255,7 @@ struct swap_info_struct { unsigned long nr_clusters_mapped; /* currently mapped cluster count */ unsigned long nr_free_tail; /* contiguous free clusters at tail */ struct dentry *debugfs_entry; /* debugfs: type_max_clusters */ + struct work_struct xswap_shrink_work; /* deferred shrink trigger */ struct mutex xswap_lock; /* serialize map/unmap operations */ #endif struct list_head free_clusters; /* free clusters list */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 265f2bac1a12..ca406556626e 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -127,11 +127,8 @@ static ssize_t xswap_max_clusters_write(struct file *file, spin_unlock(&swap_lock); } - /* - * Lowering the ceiling may make tail clusters eligible for - * shrinking. Trigger an immediate check. - */ - xswap_try_shrink(si); + /* Shrink trigger: lowering the ceiling may free tail clusters. */ + schedule_work(&si->xswap_shrink_work); return count; } @@ -726,7 +723,7 @@ static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info ci->order = 0; #ifdef CONFIG_XSWAP xswap_update_free_tail(si, ci - si->cluster_info); - xswap_try_shrink(si); + schedule_work(&si->xswap_shrink_work); #endif } @@ -3236,6 +3233,7 @@ static void free_swap_cluster_info(struct swap_info_struct *si) #ifdef CONFIG_XSWAP if (si->flags & SWP_XSWAP) { xswap_debugfs_del(si); + cancel_work_sync(&si->xswap_shrink_work); /* Unmap all mapped clusters and free the VM_SPARSE area */ if (si->nr_clusters_mapped > 0) xswap_unmap_clusters(si, 0, si->nr_clusters_mapped); @@ -4057,6 +4055,13 @@ static void xswap_trim_free_tail(struct swap_info_struct *si, unsigned long idx) WRITE_ONCE(si->nr_free_tail, nr_mapped - idx - 1); } +static void xswap_shrink_work_fn(struct work_struct *work) +{ + struct swap_info_struct *si = container_of(work, + struct swap_info_struct, xswap_shrink_work); + xswap_try_shrink(si); +} + /* * Try to shrink the cluster_info tail. Uses si->nr_free_tail which * is maintained incrementally during alloc/free — no scanning needed. @@ -4163,7 +4168,9 @@ static int setup_swap_clusters_info(struct swap_info_struct *si, /* All mapped clusters except cluster 0 are free at the tail */ si->nr_free_tail = si->nr_clusters_mapped - 1; + mutex_init(&si->xswap_lock); + INIT_WORK(&si->xswap_shrink_work, xswap_shrink_work_fn); xswap_debugfs_add(si); return 0; -- 2.54.0