Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection




On Thu, 16 Apr 2009, Steven Rostedt wrote:
I reverted my patch and added recursion detection, but I hit this nasty
bug:

---------------------------------
CPU 0
Modules linked in: radeon drm autofs4 hidp rfcomm l2cap bluetooth sunrpc
ip6t_REJECT ip6table_filter ip6_tables ipv6 sbs sbshc battery sg evbug
ide_cd_mod cdrom snd_intel8x0 snd_ac97_codec ac97_bus serio_raw
snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device
snd_pcm_oss snd_mixer_oss e1000 snd_pcm button floppy snd_timer i2c_i801
snd soundcore i2c_core snd_page_alloc ata_generic iTCO_wdt
iTCO_vendor_support pata_acpi e752x_edac edac_core pcspkr dm_snapshot
dm_zero dm_mirror dm_region_hash dm_log dm_mod ata_piix libata sd_mod
scsi_mod ext3 jbd ehci_hcd ohci_hcd uhci_hcd
Pid: 3301, comm: pcscd Tainted: G W 2.6.30-rc1 #1036 Precision
WorkStation 470
RIP: 0010:[<ffffffff803a59a2>] [<ffffffff803a59a2>] strlen+0x2/0x20
RSP: 0018:ffff880033d19c40 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffffffff807617df RCX: ffffffff807617de
RDX: ffff880033d19d48 RSI: ffff880033d19c58 RDI: 5b5b5b5b5b5b5b5b
RBP: ffff880033d19ca8 R08: 5b5b5b5b5b5b5b00 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000202 R12: 0000000000000000
R13: 5b5b5b5b5b5b5b5b R14: ffffffff81269b62 R15: ffff880033d19d08
FS: 0000000041b6f940(0063) GS:ffffffff80828000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000006aec88 CR3: 0000000033c02000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
Process pcscd (pid: 3301, threadinfo ffff880033d18000, task
ffff880033c48000)
Stack:
ffffffff803a73e5 ffffffff81269b60 ffffffff8126ab60 0000000000000004
0000000affffffff ffffffffffffffff 0000000000000000 ffff880033d19c98
0000000000000246 ffff880033d19d08 0000000000000000 0000000000000000
Call Trace:
[<ffffffff803a73e5>] ? vbin_printf+0x1b5/0x2e0
[<ffffffff802b77dc>] trace_vbprintk+0xbc/0x1c0
[<ffffffff802887fe>] ? lock_acquire+0x10e/0x120
[<ffffffff802bad29>] __trace_bprintk+0x79/0x80
[<ffffffff80228ed6>] ? ftrace_call+0x5/0x2b
[<ffffffff802b5dac>] ? tracing_record_cmdline+0x2c/0x100
[<ffffffff80284920>] ftrace_event_lock_acquire+0x60/0x70
[<ffffffff802887fe>] lock_acquire+0x10e/0x120
[<ffffffff8030a744>] ? dput+0x64/0x170
[<ffffffff80610336>] _spin_lock+0x36/0x70
[<ffffffff8030a744>] ? dput+0x64/0x170
[<ffffffff8039f98f>] ? _atomic_dec_and_lock+0x1f/0x50
[<ffffffff8030a744>] dput+0x64/0x170
[<ffffffff80315215>] dcache_dir_close+0x15/0x20
[<ffffffff802f8a51>] __fput+0xd1/0x230
[<ffffffff802f8f0b>] fput+0x1b/0x30
[<ffffffff802f566d>] filp_close+0x5d/0x90
[<ffffffff802f5746>] sys_close+0xa6/0x110
[<ffffffff802291af>] system_call_fastpath+0x16/0x1b
Code: 01 48 83 f9 ff 0f 1f 40 00 74 0b 48 83 c7 01 0f b6 07 84 c0 75 e3 c9
31 c0 c3 c9 48 89 f8 c3 66 2e 0f 1f 84 00 00 00 00 00 31 c0 <80> 3f 00 55
48 89 e5 74 11 48 89 f8 66 90 48 83 c0 01 80 38 00
RIP [<ffffffff803a59a2>] strlen+0x2/0x20
RSP <ffff880033d19c40>


Doing an objdump:

ffffffff803a59a0 <strlen>:
ffffffff803a59a0: 31 c0 xor %eax,%eax
ffffffff803a59a2: 80 3f 00 cmpb $0x0,(%rdi)
ffffffff803a59a5: 55 push %rbp
ffffffff803a59a6: 48 89 e5 mov %rsp,%rbp
ffffffff803a59a9: 74 11 je ffffffff803a59bc <strlen+0x1c>

The %rdi is: 5b5b5b5b5b5b5b5b

Either there's a bug in the vbin_printf, or we have some crazy lock->name?

TRACE_FORMAT(lock_acquire,
TP_PROTO(struct lockdep_map *lock, unsigned int subclass,
int trylock, int read, int check,
struct lockdep_map *next_lock, unsigned long ip),
TP_ARGS(lock, subclass, trylock, read, check, next_lock, ip),
TP_FMT("%s%s%s", trylock ? "try " : "",
read ? "read " : "", lock->name)
);

I'll continue to look into this, and perhaps reboot and see what other
nasties I hit.

OK, I think I figured this bug out. This is a lockdep issue with respect
to tracepoints.

The trace points in lockdep are called all the time. Outside the lockdep
logic. But if lockdep were to trigger an error / warning (which this run
did) we might be in trouble. For new locks, like the dentry->d_lock, that
are created, they will not get a name:

void lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass)
{
if (unlikely(!debug_locks))
return;

When a problem is found by lockdep, debug_locks becomes false. Thus we
stop allocating names for locks. This dentry->d_lock I had, now has no
name. Worse yet, I have CONFIG_DEBUG_VM set, that scrambles non
initialized memory. Thus, when the trace point was hit, it had junk for
the lock->name, and the machine crashed.


-- Steve

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages