On 11/28/17 11:20 AM, Waiman Long wrote:
> On 11/28/2017 02:13 PM, Yang Shi wrote:
>> Sorry for the typo, it should be v2 in the subject.
>>
>> Yang
>>
>>
>> On 11/28/17 11:12 AM, Yang Shi wrote:
>>> There are nested loops on debug objects free path, sometimes it may take
>>> over hundred thousands of loops, then cause soft lockup with
>>> !CONFIG_PREEMPT
>>> occasionally, like below:
>>>
>>> NMI watchdog: BUG: soft lockup - CPU#15 stuck for 22s!
>>> [stress-ng-getde:110342]
>>> Modules linked in: binfmt_misc(E) tcp_diag(E)
>>> inet_diag(E) bonding(E) intel_rapl(E) iosf_mbi(E)
>>> x86_pkg_temp_thermal(E) coretemp(E) iTCO_wdt(E) iTCO_vendor_support(E)
>>> kvm_intel(E) kvm(E) irqbypass(E) crct10dif_pclmul(E) crc32_pclmul(E)
>>> dcdbas(E) ghash_clmulni_intel(E) aesni_intel(E) lrw(E) gf128mul(E)
>>> glue_helper(E) ablk_helper(E) ipmi_devintf(E) sg(E) cryptd(E) pcspkr(E)
>>> mei_me(E) lpc_ich(E) ipmi_si(E) mfd_core(E) mei(E) shpchp(E) wmi(E)
>>> ipmi_msghandler(E) acpi_power_meter(E) nfsd(E) auth_rpcgss(E) nfs_acl(E)
>>> lockd(E) grace(E) sunrpc(E) ip_tables(E) ext4(E) jbd2(E) mbcache(E)
>>> sd_mod(E) mgag200(E) igb(E) drm_kms_helper(E) ixgbe(E) syscopyarea(E)
>>> mdio(E) sysfillrect(E) sysimgblt(E) ptp(E) fb_sys_fops(E) pps_core(E)
>>> ttm(E) drm(E) crc32c_intel(E) i2c_algo_bit(E) i2c_core(E)
>>> megaraid_sas(E)
>>> dca(E)
>>> irq event stamp: 4340444
>>> hardirqs last enabled at (4340443): [<ffffffff817d6476>]
>>> _raw_spin_unlock_irqrestore+0x36/0x60
>>> hardirqs last disabled at (4340444): [<ffffffff817d8c81>]
>>> apic_timer_interrupt+0x91/0xa0
>>> softirqs last enabled at (4340398): [<ffffffff817da179>]
>>> __do_softirq+0x349/0x50e
>>> softirqs last disabled at (4340391): [<ffffffff810a5255>]
>>> irq_exit+0xf5/0x110
>>> CPU: 15 PID: 110342 Comm: stress-ng-getde Tainted: G
>>> E 4.9.44-003.ali3000.alios7.x86_64.debug #1
>>> Hardware name: Dell Inc. PowerEdge R720xd/0X6FFV, BIOS
>>> 1.6.0 03/07/2013
>>> task: ffff884cbb0d0000 task.stack: ffff884cabc70000
>>> RIP: 0010:[<ffffffff817d647b>] [<ffffffff817d647b>]
>>> _raw_spin_unlock_irqrestore+0x3b/0x60
>>> RSP: 0018:ffff884cabc77b78 EFLAGS: 00000292
>>> RAX: ffff884cbb0d0000 RBX: 0000000000000292 RCX: 0000000000000000
>>> RDX: ffff884cbb0d0000 RSI: 0000000000000001 RDI: 0000000000000292
>>> RBP: ffff884cabc77b88 R08: 0000000000000000 R09: 0000000000000000
>>> R10: 0000000000000001 R11: 0000000000000001 R12: ffffffff8357a0d8
>>> R13: ffff884cabc77bc8 R14: ffffffff8357a0d0 R15: 00000000000000fc
>>> FS: 00002aee845fd2c0(0000) GS:ffff8852bd400000(0000)
>>> knlGS:0000000000000000
>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000000002991808 CR3: 0000005123abf000 CR4: 00000000000406e0
>>> Stack:
>>> ffff884ff4fe0000 ffff884ff4fd8000 ffff884cabc77c00 ffffffff8141177e
>>> 0000000000000202 ffff884cbb0d0000 ffff884cabc77bc8 0000000000000006
>>> ffff884ff4fda000 ffffffff8357a0d8 0000000000000000 91f5d976f6020b6c
>>> Call Trace:
>>> [<ffffffff8141177e>] debug_check_no_obj_freed+0x13e/0x220
>>> [<ffffffff811f8751>] __free_pages_ok+0x1f1/0x5c0
>>> [<ffffffff811fa785>] __free_pages+0x25/0x40
>>> [<ffffffff812638db>] __free_slab+0x19b/0x270
>>> [<ffffffff812639e9>] discard_slab+0x39/0x50
>>> [<ffffffff812679f7>] __slab_free+0x207/0x270
>>> [<ffffffff81269966>] ___cache_free+0xa6/0xb0
>>> [<ffffffff8126c267>] qlist_free_all+0x47/0x80
>>> [<ffffffff8126c5a9>] quarantine_reduce+0x159/0x190
>>> [<ffffffff8126b3bf>] kasan_kmalloc+0xaf/0xc0
>>> [<ffffffff8126b8a2>] kasan_slab_alloc+0x12/0x20
>>> [<ffffffff81265e8a>] kmem_cache_alloc+0xfa/0x360
>>> [<ffffffff812abc8f>] ? getname_flags+0x4f/0x1f0
>>> [<ffffffff812abc8f>] getname_flags+0x4f/0x1f0
>>> [<ffffffff812abe42>] getname+0x12/0x20
>>> [<ffffffff81298da9>] do_sys_open+0xf9/0x210
>>> [<ffffffff81298ede>] SyS_open+0x1e/0x20
>>> [<ffffffff817d6e01>] entry_SYSCALL_64_fastpath+0x1f/0xc2
>>> Code: 7f 18 53 48 8b 55 08 48 89 f3 be 01 00 00 00 e8 3c
>>> cd 92 ff 4c 89 e7 e8 f4 0e 93 ff f6 c7 02 74 1b e8 3a ac 92 ff 48 89 df
>>> 57 9d <66> 66 90 66 90 65 ff 0d d1 ff 83 7e 5b 41 5c 5d c3 48 89 df 57
>>>
>>> The code path might be called in either atomic or non-atomic context,
>>> so touching softlockup watchdog instead of calling cond_resched() which
>>> might fall asleep. However, it is unnecessary to touch the watchdog
>>> every loop, so just touch the watchdog at every 10000 (best estimate)
>>> loops.
>>>
>>> And, introduce a new knob:
>>> /sys/kernel/debug/debug_objects/suppress_lockup.
>>> 0 value means not suppress the softlockup message by touching the
>>> watchdog, non-zero value means suppress the softlockup message.
>>> The default value is zero.
>>>
>>> Signed-off-by: Yang Shi <[email protected]>
>>> CC: Waiman Long <[email protected]>
>>> CC: Thomas Gleixner <[email protected]>
>>> ---
>>> v1 --> v2:
>>> * Added suppress_lockup knob in debugfs per Waiman's suggestion
>>>
>>> lib/debugobjects.c | 30 ++++++++++++++++++++++++++++--
>>> 1 file changed, 28 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
>>> index 166488d..f009a21 100644
>>> --- a/lib/debugobjects.c
>>> +++ b/lib/debugobjects.c
>>> @@ -19,6 +19,7 @@
>>> #include <linux/slab.h>
>>> #include <linux/hash.h>
>>> #include <linux/kmemleak.h>
>>> +#include <linux/nmi.h>
>>> #define ODEBUG_HASH_BITS 14
>>> #define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
>>> @@ -67,6 +68,8 @@ struct debug_bucket {
>>> static int debug_objects_allocated;
>>> static int debug_objects_freed;
>>> +static int suppress_lockup;
>>> +
>>> static void free_obj_work(struct work_struct *work);
>>> static DECLARE_WORK(debug_obj_work, free_obj_work);
>>> @@ -768,6 +771,10 @@ static void __debug_check_no_obj_freed(const
>>> void *address, unsigned long size)
>>> debug_objects_maxchain = cnt;
>>> max_loops += cnt;
>>> +
>>> + if (max_loops > 10000 && ((max_loops % 10000) == 0)
>>> + && suppress_lockup != 0)
>>> + touch_softlockup_watchdog();
>>> }
>>> if (max_loops > debug_objects_maxloops)
>>> @@ -810,9 +817,23 @@ static int debug_stats_open(struct inode *inode,
>>> struct file *filp)
>>> .release = single_release,
>>> };
>>> +static int suppress_lockup_get(void *data, u64 *val)
>>> +{
>>> + *val = (u64) suppress_lockup;
>>> + return 0;
>>> +}
>>> +
>>> +static int suppress_lockup_set(void *data, u64 val)
>>> +{
>>> + suppress_lockup = (u32) val;
>>> + return 0;
>>> +}
>>> +DEFINE_DEBUGFS_ATTRIBUTE(suppress_lockup_fops,
>>> + suppress_lockup_get, suppress_lockup_set, "%llu\n");
>>> +
>>> static int __init debug_objects_init_debugfs(void)
>>> {
>>> - struct dentry *dbgdir, *dbgstats;
>>> + struct dentry *dbgdir, *dbgstats, *dbglockup;
>>> if (!debug_objects_enabled)
>>> return 0;
>>> @@ -826,10 +847,15 @@ static int __init debug_objects_init_debugfs(void)
>>> if (!dbgstats)
>>> goto err;
>>> + dbglockup = debugfs_create_file_unsafe("suppress_lockup",
>>> 0644, dbgdir,
>>> + NULL, &suppress_lockup_fops);
>>> + if (!dbglockup)
>>> + goto err;
>>> +
>
> It is actually easier to use helper function like debugfs_create_u32()
> to create the file without defining any file ops.
Aha, thanks for mentioning the helper API. Will adopt the API in v3.
Regards,
Yang
>
> Cheers,
> Longman
>
From 1585338898023518006@xxx Tue Nov 28 19:23:09 +0000 2017
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