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Subject[PATCH 4/4 v6] lib: debugobjects: handle objects free in a batch outside the loop
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]

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

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

The code path might be called in either atomic or non-atomic context,
and in_atomic() can't tell if current context is atomic or not on
!PREEMPT kernel, so cond_resched() can't be used to prevent from the
softlockup.

Utilize the global free list to defer objects free outside of the loop in
a batch to save some cycles in the loop.

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
---
lib/debugobjects.c | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 09f2469..b1b42bd 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -776,12 +776,12 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size)
{
unsigned long flags, oaddr, saddr, eaddr, paddr, chunks;
struct hlist_node *tmp;
- HLIST_HEAD(freelist);
struct debug_obj_descr *descr;
enum debug_obj_state state;
struct debug_bucket *db;
struct debug_obj *obj;
int cnt, max_loops = 0;
+ bool work = false;

saddr = (unsigned long) address;
eaddr = saddr + size;
@@ -812,18 +812,12 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size)
goto repeat;
default:
hlist_del(&obj->node);
- hlist_add_head(&obj->node, &freelist);
+ work |= __free_object(obj);
break;
}
}
raw_spin_unlock_irqrestore(&db->lock, flags);

- /* Now free them */
- hlist_for_each_entry_safe(obj, tmp, &freelist, node) {
- hlist_del(&obj->node);
- free_object(obj);
- }
-
if (cnt > debug_objects_maxchain)
debug_objects_maxchain = cnt;

@@ -832,6 +826,10 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size)

if (max_loops > debug_objects_maxloops)
debug_objects_maxloops = max_loops;
+
+ /* Schedule work to move free objs to pool list */
+ if (work)
+ schedule_work(&debug_obj_work);
}

void debug_check_no_obj_freed(const void *address, unsigned long size)
--
1.8.3.1
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