Date:   Wed, 29 Nov 2017 03:13:37 +0800
From:   "Yang Shi" <yang.s@...baba-inc.com>
To:     longman@...hat.com, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 v8] lib: debugobjects: touch watchdog to avoid
 softlockup when !CONFIG_PREEMPT

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 <yang.s@...baba-inc.com>
> CC: Waiman Long <longman@...hat.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> ---
> 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;
> +
>   	return 0;
>   
>   err:
> -	debugfs_remove(dbgdir);
> +	debugfs_remove_recursive(dbgdir);
>   
>   	return -ENOMEM;
>   }
> 

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