From: Gao Xiang hsiangkao@linux.alibaba.com
next inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IAHY3K
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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/20240729021306.398286-1-hsiangkao@linux.alibaba.co... Fixes: 5dfab109d519 ("migrate_pages: batch _unmap and _move") Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com Reviewed-by: "Huang, Ying" ying.huang@intel.com Acked-by: David Hildenbrand david@redhat.com Cc: Matthew Wilcox willy@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/migrate.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c index 01e04e47699c..c091060585a3 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1480,11 +1480,17 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, 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) @@ -1678,7 +1684,7 @@ 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; @@ -1700,7 +1706,7 @@ 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; @@ -1732,7 +1738,7 @@ 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;