mm/migrate: fix deadlock in migrate_pages_batch() on large folios

Currently, migrate_pages_batch() can lock multiple locked folios with an
arbitrary order.  Although folio_trylock() is used to avoid deadlock as
commit 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously
firstly") mentioned, it seems try_split_folio() is still missing.

It was found by compaction stress test when I explicitly enable EROFS
compressed files to use large folios, which case I cannot reproduce with
the same workload if large folio support is off (current mainline).
Typically, filesystem reads (with locked file-backed folios) could use
another bdev/meta inode to load some other I/Os (e.g.  inode extent
metadata or caching compressed data), so the locking order will be:

  file-backed folios  (A)
     bdev/meta folios (B)

The following calltrace shows the deadlock:
   Thread 1 takes (B) lock and tries to take folio (A) lock
   Thread 2 takes (A) lock and tries to take folio (B) lock

[Thread 1]
INFO: task stress:1824 blocked for more than 30 seconds.
      Tainted: G           OE      6.10.0-rc7+ #6
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:stress          state:D stack:0     pid:1824  tgid:1824  ppid:1822   flags:0x0000000c
Call trace:
 __switch_to+0xec/0x138
 __schedule+0x43c/0xcb0
 schedule+0x54/0x198
 io_schedule+0x44/0x70
 folio_wait_bit_common+0x184/0x3f8
			<-- folio mapping ffff00036d69cb18 index 996  (**)
 __folio_lock+0x24/0x38
 migrate_pages_batch+0x77c/0xea0	// try_split_folio (mm/migrate.c:1486:2)
					// migrate_pages_batch (mm/migrate.c:1734:16)
		<--- LIST_HEAD(unmap_folios) has
			..
			folio mapping 0xffff0000d184f1d8 index 1711;   (*)
			folio mapping 0xffff0000d184f1d8 index 1712;
			..
 migrate_pages+0xb28/0xe90
 compact_zone+0xa08/0x10f0
 compact_node+0x9c/0x180
 sysctl_compaction_handler+0x8c/0x118
 proc_sys_call_handler+0x1a8/0x280
 proc_sys_write+0x1c/0x30
 vfs_write+0x240/0x380
 ksys_write+0x78/0x118
 __arm64_sys_write+0x24/0x38
 invoke_syscall+0x78/0x108
 el0_svc_common.constprop.0+0x48/0xf0
 do_el0_svc+0x24/0x38
 el0_svc+0x3c/0x148
 el0t_64_sync_handler+0x100/0x130
 el0t_64_sync+0x190/0x198

[Thread 2]
INFO: task stress:1825 blocked for more than 30 seconds.
      Tainted: G           OE      6.10.0-rc7+ #6
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:stress          state:D stack:0     pid:1825  tgid:1825  ppid:1822   flags:0x0000000c
Call trace:
 __switch_to+0xec/0x138
 __schedule+0x43c/0xcb0
 schedule+0x54/0x198
 io_schedule+0x44/0x70
 folio_wait_bit_common+0x184/0x3f8
			<-- folio = 0xfffffdffc6b503c0 (mapping == 0xffff0000d184f1d8 index == 1711) (*)
 __folio_lock+0x24/0x38
 z_erofs_runqueue+0x384/0x9c0 [erofs]
 z_erofs_readahead+0x21c/0x350 [erofs]       <-- folio mapping 0xffff00036d69cb18 range from [992, 1024] (**)
 read_pages+0x74/0x328
 page_cache_ra_order+0x26c/0x348
 ondemand_readahead+0x1c0/0x3a0
 page_cache_sync_ra+0x9c/0xc0
 filemap_get_pages+0xc4/0x708
 filemap_read+0x104/0x3a8
 generic_file_read_iter+0x4c/0x150
 vfs_read+0x27c/0x330
 ksys_pread64+0x84/0xd0
 __arm64_sys_pread64+0x28/0x40
 invoke_syscall+0x78/0x108
 el0_svc_common.constprop.0+0x48/0xf0
 do_el0_svc+0x24/0x38
 el0_svc+0x3c/0x148
 el0t_64_sync_handler+0x100/0x130
 el0t_64_sync+0x190/0x198

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 5dfab109d519 ("migrate_pages: batch _unmap and _move")
Signed-off-by: Gao Xiang <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

diff --git a/mm/migrate.c b/mm/migrate.c
index e7296c0fb5d57a2ee8585fca9e0a031be090f97f..923ea80ba7442b82c58f4a1680a77562ee154f98 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1479,11 +1479,17 @@ out:
        return rc;
 }
 
-static inline int try_split_folio(struct folio *folio, struct list_head *split_folios)
+static inline int try_split_folio(struct folio *folio, struct list_head *split_folios,
+                                 enum migrate_mode mode)
 {
        int rc;
 
-       folio_lock(folio);
+       if (mode == MIGRATE_ASYNC) {
+               if (!folio_trylock(folio))
+                       return -EAGAIN;
+       } else {
+               folio_lock(folio);
+       }
        rc = split_folio_to_list(folio, split_folios);
        folio_unlock(folio);
        if (!rc)
@@ -1677,7 +1683,7 @@ static int migrate_pages_batch(struct list_head *from,
                         */
                        if (nr_pages > 2 &&
                           !list_empty(&folio->_deferred_list)) {
-                               if (try_split_folio(folio, split_folios) == 0) {
+                               if (!try_split_folio(folio, split_folios, mode)) {
                                        nr_failed++;
                                        stats->nr_thp_failed += is_thp;
                                        stats->nr_thp_split += is_thp;
@@ -1699,7 +1705,7 @@ static int migrate_pages_batch(struct list_head *from,
                        if (!thp_migration_supported() && is_thp) {
                                nr_failed++;
                                stats->nr_thp_failed++;
-                               if (!try_split_folio(folio, split_folios)) {
+                               if (!try_split_folio(folio, split_folios, mode)) {
                                        stats->nr_thp_split++;
                                        stats->nr_split++;
                                        continue;
@@ -1731,7 +1737,7 @@ static int migrate_pages_batch(struct list_head *from,
                                stats->nr_thp_failed += is_thp;
                                /* Large folio NUMA faulting doesn't split to retry. */
                                if (is_large && !nosplit) {
-                                       int ret = try_split_folio(folio, split_folios);
+                                       int ret = try_split_folio(folio, split_folios, mode);
 
                                        if (!ret) {
                                                stats->nr_thp_split += is_thp;