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Subject[PATCH 2/2 v3] lib: debugobjects: touch watchdog to avoid softlockup when !CONFIG_PREEMPT
Date
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;
}
--
1.8.3.1
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