Recently, We test an linux 4.19 stable and find the following issue. kernel BUG at lib/radix-tree.c:1429! invalid opcode: 0000 [#1] SMP KASAN PTI CPU: 7 PID: 6935 Comm: syz-executor.2 Not tainted 4.19.36 #25 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 RIP: 0010:radix_tree_tag_set+0x200/0x2f0 lib/radix-tree.c:1429 Code: 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 89 44 24 10 e8 a3 29 7e fe 48 8b 44 24 10 48 0f ab 03 e9 d2 fe ff ff e8 90 29 7e fe <0f> 0b 48 c7 c7 e0 5a 87 84 e8 f0 e7 08 ff 4c 89 ef e8 4a ff ac fe RSP: 0018:ffff88837b13fb60 EFLAGS: 00010016 RAX: 0000000000040000 RBX: ffff8883c5515d58 RCX: ffffffff82cb2ef0 RDX: 0000000000000b72 RSI: ffffc90004cf2000 RDI: ffff8883c5515d98 RBP: ffff88837b13fb98 R08: ffffed106f627f7e R09: ffffed106f627f7e R10: 0000000000000001 R11: ffffed106f627f7d R12: 0000000000000004 R13: ffffea000d7fea80 R14: 1ffff1106f627f6f R15: 0000000000000002 FS: 00007fa1b8df2700(0000) GS:ffff8883e2fc0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa1b8df1db8 CR3: 000000037d4d2001 CR4: 0000000000160ee0 Call Trace: memfd_tag_pins mm/memfd.c:51 [inline] memfd_wait_for_pins+0x2c5/0x12d0 mm/memfd.c:81 memfd_add_seals mm/memfd.c:215 [inline] memfd_fcntl+0x33d/0x4a0 mm/memfd.c:247 do_fcntl+0x589/0xeb0 fs/fcntl.c:421 __do_sys_fcntl fs/fcntl.c:463 [inline] __se_sys_fcntl fs/fcntl.c:448 [inline] __x64_sys_fcntl+0x12d/0x180 fs/fcntl.c:448 do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:293 By reviewing the code, I find that there is an race between iterate the radix_tree and radix_tree_insert/delete. Because the former just access its slot in rcu protected period. but it fails to prevent the radix_tree from being changed. Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx> --- mm/memfd.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/mm/memfd.c b/mm/memfd.c index 2bb5e25..0b3fedc 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -37,8 +37,8 @@ static void memfd_tag_pins(struct address_space *mapping) lru_add_drain(); start = 0; - rcu_read_lock(); + xa_lock_irq(&mapping->i_pages); radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) { page = radix_tree_deref_slot(slot); if (!page || radix_tree_exception(page)) { @@ -47,18 +47,16 @@ static void memfd_tag_pins(struct address_space *mapping) continue; } } else if (page_count(page) - page_mapcount(page) > 1) { - xa_lock_irq(&mapping->i_pages); radix_tree_tag_set(&mapping->i_pages, iter.index, MEMFD_TAG_PINNED); - xa_unlock_irq(&mapping->i_pages); } if (need_resched()) { slot = radix_tree_iter_resume(slot, &iter); - cond_resched_rcu(); + cond_resched_lock(&mapping->i_pages.xa_lock); } } - rcu_read_unlock(); + xa_unlock_irq(&mapping->i_pages); } /* -- 1.7.12.4