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SubjectRe: [PATCH 2/2 v3] lib: debugobjects: touch watchdog to avoid softlockup when !CONFIG_PREEMPT
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Hi Thomas,

Waiman has reviewed the patches, any comment from you is appreciated.

Thanks,
Yang

On 11/28/17 12:24 PM, Waiman Long wrote:
> On 11/28/2017 02:45 PM, 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 <yang.s@alibaba-inc.com>
>> CC: Waiman Long <longman@redhat.com>
>> CC: Thomas Gleixner <tglx@linutronix.de>
>> ---
>> v2 --> v3:
>> * Use debugfs_create_u32() helper API per Waiman's suggestion
>> v1 --> v2:
>> * Added suppress_lockup knob in debugfs per Waiman's suggestion
>>
>> lib/debugobjects.c | 16 ++++++++++++++--
>> 1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
>> index 166488d..c960221 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)
>> @@ -812,7 +819,7 @@ static int debug_stats_open(struct inode *inode, struct file *filp)
>>
>> 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 +833,15 @@ static int __init debug_objects_init_debugfs(void)
>> if (!dbgstats)
>> goto err;
>>
>> + dbglockup = debugfs_create_u32("suppress_lockup", 0644, dbgdir,
>> + &suppress_lockup);
>> + if (!dbglockup)
>> + goto err;
>> +
>> return 0;
>>
>> err:
>> - debugfs_remove(dbgdir);
>> + debugfs_remove_recursive(dbgdir);
>>
>> return -ENOMEM;
>> }
>
> I am OK with your patch. Now it is up to Thomas to decide if he will
> pick up your patch.
>
> Cheers,
> Longman
>

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