Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 19 Nov 2020 13:33:21 +0100 | Subject | Re: [PATCH v3] lockdep: Allow tuning tracing capacity constants. |
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On Wed, Nov 18, 2020 at 4:32 PM Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote: > > On 2020/11/19 0:10, Peter Zijlstra wrote: > > On Wed, Nov 18, 2020 at 11:30:05PM +0900, Tetsuo Handa wrote: > >> The problem is that we can't know what exactly is consuming these resources. > >> My question is do you have a plan to make it possible to know what exactly is > >> consuming these resources. > > > > I'm pretty sure it's in /proc/lockdep* somewhere. > > OK. Then... > > Dmitry, can you update syzkaller to dump /proc/lockdep* before terminating as > a crash as soon as encountering one of > > BUG: MAX_LOCKDEP_ENTRIES too low! > BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! > BUG: MAX_LOCKDEP_CHAINS too low! > BUG: MAX_LOCKDEP_KEYS too low! > WARNING in print_bfs_bug > > messages? > > On 2020/09/16 21:14, Dmitry Vyukov wrote: > > On Wed, Sep 16, 2020 at 1:51 PM <peterz@infradead.org> wrote: > >> > >> On Wed, Sep 16, 2020 at 01:28:19PM +0200, Dmitry Vyukov wrote: > >>> On Fri, Sep 4, 2020 at 6:05 PM Tetsuo Handa > >>> <penguin-kernel@i-love.sakura.ne.jp> wrote: > >>>> > >>>> Hello. Can we apply this patch? > >>>> > >>>> This patch addresses top crashers for syzbot, and applying this patch > >>>> will help utilizing syzbot's resource for finding other bugs. > >>> > >>> Acked-by: Dmitry Vyukov <dvyukov@google.com> > >>> > >>> Peter, do you still have concerns with this? > >> > >> Yeah, I still hate it with a passion; it discourages thinking. A bad > >> annotation that blows up the lockdep storage, no worries, we'll just > >> increase this :/ > >> > >> IIRC the issue with syzbot is that the current sysfs annotation is > >> pretty terrible and generates a gazillion classes, and syzbot likes > >> poking at /sys a lot and thus floods the system. > >> > >> I don't know enough about sysfs to suggest an alternative, and haven't > >> exactly had spare time to look into it either :/ > >> > >> Examples of bad annotations is getting every CPU a separate class, that > >> leads to nr_cpus! chains if CPUs arbitrarily nest (nr_cpus^2 if there's > >> only a single nesting level). > > > > Maybe on "BUG: MAX_LOCKDEP_CHAINS too low!" we should then aggregate, > > sort and show existing chains so that it's possible to identify if > > there are any worst offenders and who they are. > > > > Currently we only have a hypothesis that there are some worst > > offenders vs lots of normal load. And we can't point fingers which > > means that, say, sysfs, or other maintainers won't be too inclined to > > fix anything. > > > > If we would know for sure that lock class X is guilty. That would make > > the situation much more actionable.
I am trying to reproduce this locally first. syzbot caims it can reproduce it with a number of very simpler reproducers (like spawn process, unshare, create socket): https://syzkaller.appspot.com/bug?id=8a18efe79140782a88dcd098808d6ab20ed740cc
I see a very slow drift, but it's very slow, so get only to: direct dependencies: 22072 [max: 32768]
But that's running a very uniform workload.
However when I tried to cat /proc/lockdep to see if there is anything fishy already, I got this (on c2e7554e1b85935d962127efa3c2a76483b0b3b6).
Some missing locks?
================================================================== BUG: KASAN: use-after-free in string_nocheck lib/vsprintf.c:611 [inline] BUG: KASAN: use-after-free in string+0x39c/0x3d0 lib/vsprintf.c:693 Read of size 1 at addr ffff888295833740 by task less/1855
CPU: 0 PID: 1855 Comm: less Tainted: G W 5.10.0-rc4+ #68 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-44-g88ab0c15525c-prebuilt.qemu.org 04/01/2014 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x107/0x163 lib/dump_stack.c:118 print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385 __kasan_report mm/kasan/report.c:545 [inline] kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562 string_nocheck lib/vsprintf.c:611 [inline] string+0x39c/0x3d0 lib/vsprintf.c:693 vsnprintf+0x71b/0x14f0 lib/vsprintf.c:2618 seq_vprintf fs/seq_file.c:398 [inline] seq_printf+0x195/0x240 fs/seq_file.c:413 print_name+0x98/0x1d0 kernel/locking/lockdep_proc.c:50 l_show+0x111/0x2c0 kernel/locking/lockdep_proc.c:82 seq_read_iter+0xae4/0x10c0 fs/seq_file.c:268 proc_reg_read_iter+0x1fb/0x2d0 fs/proc/inode.c:310 call_read_iter include/linux/fs.h:1897 [inline] new_sync_read+0x41e/0x6e0 fs/read_write.c:415 vfs_read+0x35c/0x570 fs/read_write.c:496 ksys_read+0x12d/0x250 fs/read_write.c:634 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f1d48906310 Code: 73 01 c3 48 8b 0d 28 4b 2b 00 31 d2 48 29 c2 64 89 11 48 83 c8 ff eb ea 90 90 83 3d e5 a2 2b 00 00 75 10 b8 00 00 00 00 0f 05 <48> 3d 01 f04 RSP: 002b:00007fff8ad3f048 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: 0000000000ae0ec0 RCX: 00007f1d48906310 RDX: 0000000000002000 RSI: 0000000000ae0eec RDI: 0000000000000004 RBP: 0000000000072000 R08: 0000000000000038 R09: 0000000001000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000a6d7f0 R13: 0000000000000000 R14: 0000000000000039 R15: 0000000000ae0ec0
Allocated by task 2828: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48 kasan_set_track mm/kasan/common.c:56 [inline] __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:461 kmalloc include/linux/slab.h:557 [inline] kzalloc include/linux/slab.h:664 [inline] tomoyo_encode2.part.0+0xe9/0x3a0 security/tomoyo/realpath.c:45 tomoyo_encode2 security/tomoyo/realpath.c:31 [inline] tomoyo_encode+0x28/0x50 security/tomoyo/realpath.c:80 tomoyo_path_perm+0x368/0x400 security/tomoyo/file.c:831 tomoyo_path_symlink+0x94/0xe0 security/tomoyo/tomoyo.c:200 security_path_symlink+0xdf/0x150 security/security.c:1110 do_symlinkat+0x123/0x2c0 fs/namei.c:3985 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9
Freed by task 2828: kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48 kasan_set_track+0x1c/0x30 mm/kasan/common.c:56 kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:355 __kasan_slab_free+0x102/0x140 mm/kasan/common.c:422 slab_free_hook mm/slub.c:1544 [inline] slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1577 slab_free mm/slub.c:3142 [inline] kfree+0xdb/0x360 mm/slub.c:4124 tomoyo_path_perm+0x3b0/0x400 security/tomoyo/file.c:840 tomoyo_path_symlink+0x94/0xe0 security/tomoyo/tomoyo.c:200 security_path_symlink+0xdf/0x150 security/security.c:1110 do_symlinkat+0x123/0x2c0 fs/namei.c:3985 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xa9
The buggy address belongs to the object at ffff888295833740 which belongs to the cache kmalloc-32 of size 32 The buggy address is located 0 bytes inside of 32-byte region [ffff888295833740, ffff888295833760) The buggy address belongs to the page: page:00000000706b2f94 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x295833 flags: 0x57ffe0000000200(slab) raw: 057ffe0000000200 ffffea0004adca40 0000000200000002 ffff888100041a00 raw: 0000000000000000 0000000000400040 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff888295833600: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc ffff888295833680: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc >ffff888295833700: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc ^ ffff888295833780: 00 00 00 fc fc fc fc fc 00 00 00 fc fc fc fc fc ffff888295833800: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc ==================================================================
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