On 07.07.2018 10:16, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 526674536360 Add linux-next specific files for 20180706 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=13853f48400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=c8d1cfc0cb798e48 > dashboard link: https://syzkaller.appspot.com/bug?extid=93c67806397421af04d5 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+93c67806397421af04d5@xxxxxxxxxxxxxxxxxxxxxxxxx > > ------------[ cut here ]------------ > kernel BUG at mm/vmscan.c:593! > invalid opcode: 0000 [#1] SMP KASAN > CPU: 0 PID: 5039 Comm: syz-executor5 Not tainted 4.18.0-rc3-next-20180706+ #1 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:shrink_slab_memcg mm/vmscan.c:593 [inline] > RIP: 0010:shrink_slab+0xb3e/0xdb0 mm/vmscan.c:672 > Code: 8d a8 fd ff ff f0 48 0f b3 08 e8 3d b8 da ff 48 8b 85 c0 fd ff ff c7 00 f8 f8 f8 f8 c6 40 04 f8 e9 5d fb ff ff e8 22 b8 da ff <0f> 0b e8 1b b8 da ff 48 8b 9d d8 fd ff ff 31 ff 48 89 de e8 3a b9 > RSP: 0018:ffff88019aa0eb50 EFLAGS: 00010212 > RAX: 0000000000040000 RBX: ffff88019aa0eda0 RCX: ffffc90001e24000 > RDX: 0000000000000b7a RSI: ffffffff81a1c23e RDI: 0000000000000007 > RBP: ffff88019aa0edc8 R08: ffff88019ed86340 R09: ffffed00399ff4b8 > R10: ffffed00399ff4b8 R11: ffff8801ccffa5c7 R12: dffffc0000000000 > R13: ffff8801cc3231f0 R14: 0000000000000000 R15: ffff88019aa0ebe0 > FS: 00007fa51a834700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fa51a803008 CR3: 00000001ad011000 CR4: 00000000001406f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > shrink_node+0x429/0x16a0 mm/vmscan.c:2736 > shrink_zones mm/vmscan.c:2965 [inline] > do_try_to_free_pages+0x3e7/0x1290 mm/vmscan.c:3027 > try_to_free_mem_cgroup_pages+0x49d/0xc90 mm/vmscan.c:3325 > memory_high_write+0x283/0x310 mm/memcontrol.c:5597 > cgroup_file_write+0x31f/0x840 kernel/cgroup/cgroup.c:3500 > kernfs_fop_write+0x2ba/0x480 fs/kernfs/file.c:316 > __vfs_write+0x117/0x9f0 fs/read_write.c:485 > __kernel_write+0x10c/0x370 fs/read_write.c:506 > write_pipe_buf+0x181/0x240 fs/splice.c:798 > splice_from_pipe_feed fs/splice.c:503 [inline] > __splice_from_pipe+0x38e/0x7c0 fs/splice.c:627 > splice_from_pipe+0x1ea/0x340 fs/splice.c:662 > default_file_splice_write+0x3c/0x90 fs/splice.c:810 > do_splice_from fs/splice.c:852 [inline] > direct_splice_actor+0x128/0x190 fs/splice.c:1019 > splice_direct_to_actor+0x318/0x8f0 fs/splice.c:974 > do_splice_direct+0x2d4/0x420 fs/splice.c:1062 > do_sendfile+0x62a/0xe20 fs/read_write.c:1440 > __do_sys_sendfile64 fs/read_write.c:1495 [inline] > __se_sys_sendfile64 fs/read_write.c:1487 [inline] > __x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1487 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x455ba9 > Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007fa51a833c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000028 > RAX: ffffffffffffffda RBX: 00007fa51a8346d4 RCX: 0000000000455ba9 > RDX: 0000000020000040 RSI: 0000000000000015 RDI: 0000000000000015 > RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000001 R11: 0000000000000246 R12: 00000000ffffffff > R13: 00000000004c0dc5 R14: 00000000004d0e78 R15: 0000000000000000 > Modules linked in: > Dumping ftrace buffer: > (ftrace buffer empty) > ---[ end trace 607c0e9f278af1e6 ]--- > RIP: 0010:shrink_slab_memcg mm/vmscan.c:593 [inline] > RIP: 0010:shrink_slab+0xb3e/0xdb0 mm/vmscan.c:672 > Code: 8d a8 fd ff ff f0 48 0f b3 08 e8 3d b8 da ff 48 8b 85 c0 fd ff ff c7 00 f8 f8 f8 f8 c6 40 04 f8 e9 5d fb ff ff e8 22 b8 da ff <0f> 0b e8 1b b8 da ff 48 8b 9d d8 fd ff ff 31 ff 48 89 de e8 3a b9 > RSP: 0018:ffff88019aa0eb50 EFLAGS: 00010212 > RAX: 0000000000040000 RBX: ffff88019aa0eda0 RCX: ffffc90001e24000 > RDX: 0000000000000b7a RSI: ffffffff81a1c23e RDI: 0000000000000007 > RBP: ffff88019aa0edc8 R08: ffff88019ed86340 R09: ffffed00399ff4b8 > R10: ffffed00399ff4b8 R11: ffff8801ccffa5c7 R12: dffffc0000000000 > R13: ffff8801cc3231f0 R14: 0000000000000000 R15: ffff88019aa0ebe0 > FS: 00007fa51a834700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fa51a803008 CR3: 00000001ad011000 CR4: 00000000001406f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 I've found two potential places, which may result in memory problems. We need to do INIT_LIST_HEAD() before preallocation of memcg shrinker to prevent shrinker to pick it before register_shrinker_prepared() is finished. Also, nr_deffered has to be freed after the shrinker is unregistered, not before. --- diff --git a/mm/vmscan.c b/mm/vmscan.c index e385dcb278c9..f8a3b7f99132 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -362,11 +363,6 @@ int prealloc_shrinker(struct shrinker *shrinker) if (!shrinker->nr_deferred) return -ENOMEM; - if (shrinker->flags & SHRINKER_MEMCG_AWARE) { - if (prealloc_memcg_shrinker(shrinker)) - goto free_deferred; - } - /* * There is a window between prealloc_shrinker() * and register_shrinker_prepared(). We don't want @@ -381,6 +377,12 @@ int prealloc_shrinker(struct shrinker *shrinker) * is not registered (id is not assigned). */ INIT_LIST_HEAD(&shrinker->list); + + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { + if (prealloc_memcg_shrinker(shrinker)) + goto free_deferred; + } + return 0; free_deferred: @@ -394,11 +396,11 @@ void free_prealloced_shrinker(struct shrinker *shrinker) if (!shrinker->nr_deferred) return; - kfree(shrinker->nr_deferred); - shrinker->nr_deferred = NULL; - if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); + + kfree(shrinker->nr_deferred); + shrinker->nr_deferred = NULL; } void register_shrinker_prepared(struct shrinker *shrinker) @@ -569,13 +571,10 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, if (!down_read_trylock(&shrinker_rwsem)) return 0; - /* - * 1) Caller passes only alive memcg, so map can't be NULL. - * 2) shrinker_rwsem protects from maps expanding. - */ map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, true); - BUG_ON(!map); + if (unlikely(!map)) + goto unlock; for_each_set_bit(i, map->map, shrinker_nr_max) { struct shrink_control sc = { @@ -628,7 +626,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, break; } } - +unlock: up_read(&shrinker_rwsem); return freed; }
