Messages in this thread Patch in this message | | | Date | Mon, 15 Jun 2015 15:24:29 -0700 | From | Alexei Starovoitov <> | Subject | call_rcu from trace_preempt |
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Hi Paul,
I've been debugging the issue reported by Daniel: http://thread.gmane.org/gmane.linux.kernel/1974304/focus=1974304 and it seems I narrowed it down to recursive call_rcu. From trace_preempt_on() I'm doing: e = kmalloc(sizeof(struct elem), GFP_ATOMIC) kfree_rcu(e, rcu)
which causing all sorts of corruptions like: [ 2.074175] WARNING: CPU: 0 PID: 3 at ../lib/debugobjects.c:263 debug_print_object+0x8c/0xb0() [ 2.075567] ODEBUG: active_state not available (active state 0) object type: rcu_head hint: (null)
[ 2.102141] WARNING: CPU: 0 PID: 3 at ../lib/debugobjects.c:263 debug_print_object+0x8c/0xb0() [ 2.103547] ODEBUG: deactivate not available (active state 0) object type: rcu_head hint: (null)
[ 2.253995] WARNING: CPU: 0 PID: 7 at ../kernel/rcu/tree.c:2976 __call_rcu.constprop.67+0x1e5/0x350() [ 2.255510] __call_rcu(): Leaked duplicate callback
Sometimes stack looks like: [ 2.145163] WARNING: CPU: 0 PID: 102 at ../lib/debugobjects.c:263 debug_print_object+0x8c/0xb0() [ 2.147465] ODEBUG: active_state not available (active state 0) object type: rcu_head hint: (null) [ 2.148022] Modules linked in: [ 2.148022] CPU: 0 PID: 102 Comm: systemd-udevd Not tainted 4.1.0-rc7+ #653 [ 2.148022] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-rc1-0-gb1d4dc9-20140515_140003-nilsson.home.kraxel.org 04/01/2014 [ 2.148022] ffffffff81a34f77 ffff88000fc03d18 ffffffff81781ed4 0000000000000105 [ 2.148022] ffff88000fc03d68 ffff88000fc03d58 ffffffff81064e57 0000000000000000 [ 2.148022] ffff88000fc03e20 ffffffff81c50f00 ffffffff81a34fdf 0000000000000286 [ 2.148022] Call Trace: [ 2.148022] <IRQ> [<ffffffff81781ed4>] dump_stack+0x4f/0x7b [ 2.148022] [<ffffffff81064e57>] warn_slowpath_common+0x97/0xe0 [ 2.148022] [<ffffffff81064f56>] warn_slowpath_fmt+0x46/0x50 [ 2.148022] [<ffffffff813d305c>] debug_print_object+0x8c/0xb0 [ 2.148022] [<ffffffff813d3cf6>] ? debug_object_active_state+0x66/0x160 [ 2.148022] [<ffffffff813d3d81>] debug_object_active_state+0xf1/0x160 [ 2.148022] [<ffffffff810e33b1>] rcu_process_callbacks+0x301/0xae0 [ 2.148022] [<ffffffff810e3397>] ? rcu_process_callbacks+0x2e7/0xae0 [ 2.148022] [<ffffffff810e9f28>] ? run_timer_softirq+0x218/0x4c0 [ 2.148022] [<ffffffff81069dff>] __do_softirq+0x14f/0x670 [ 2.148022] [<ffffffff8106a5f5>] irq_exit+0xa5/0xb0 [ 2.148022] [<ffffffff8178ea6a>] smp_apic_timer_interrupt+0x4a/0x60 [ 2.148022] [<ffffffff8178cea0>] apic_timer_interrupt+0x70/0x80 [ 2.148022] <EOI> [<ffffffff813d363c>] ? debug_object_activate+0x9c/0x1e0 [ 2.148022] [<ffffffff8178bd47>] ? _raw_spin_unlock_irqrestore+0x67/0x80 [ 2.148022] [<ffffffff813d36f6>] debug_object_activate+0x156/0x1e0 [ 2.148022] [<ffffffff810de037>] rcuhead_fixup_activate+0x37/0x40 [ 2.148022] [<ffffffff813d36a1>] debug_object_activate+0x101/0x1e0 [ 2.148022] [<ffffffff8178bd2b>] ? _raw_spin_unlock_irqrestore+0x4b/0x80 [ 2.148022] [<ffffffff810e2d26>] __call_rcu.constprop.67+0x46/0x350 [ 2.148022] [<ffffffff813d3524>] ? __debug_object_init+0x3f4/0x430 [ 2.148022] [<ffffffff8178bd2b>] ? _raw_spin_unlock_irqrestore+0x4b/0x80 [ 2.148022] [<ffffffff810e308a>] kfree_call_rcu+0x1a/0x20 [ 2.148022] [<ffffffff8115e230>] trace_preempt_on+0x180/0x290 [ 2.148022] [<ffffffff8115e17e>] ? trace_preempt_on+0xce/0x290 [ 2.148022] [<ffffffff810991c3>] preempt_count_sub+0x73/0xf0 [ 2.148022] [<ffffffff8178bd2b>] _raw_spin_unlock_irqrestore+0x4b/0x80 [ 2.148022] [<ffffffff813d3524>] __debug_object_init+0x3f4/0x430 [ 2.148022] [<ffffffff8115e23c>] ? trace_preempt_on+0x18c/0x290 [ 2.148022] [<ffffffff813d357b>] debug_object_init+0x1b/0x20 [ 2.148022] [<ffffffff810de028>] rcuhead_fixup_activate+0x28/0x40 [ 2.148022] [<ffffffff813d36a1>] debug_object_activate+0x101/0x1e0 [ 2.148022] [<ffffffff812036b0>] ? get_max_files+0x20/0x20 [ 2.148022] [<ffffffff810e2d26>] __call_rcu.constprop.67+0x46/0x350 [ 2.148022] [<ffffffff810e30a7>] call_rcu+0x17/0x20 [ 2.148022] [<ffffffff81203903>] __fput+0x183/0x200 [ 2.148022] [<ffffffff812039ce>] ____fput+0xe/0x10 [ 2.148022] [<ffffffff81088dd5>] task_work_run+0xb5/0xe0 [ 2.148022] [<ffffffff81002c74>] do_notify_resume+0x64/0x80 [ 2.148022] [<ffffffff8178c26c>] int_signal+0x12/0x17
My reading of the code is debug_object_*() bits are reporting real problem. In the above trace the call debug_rcu_head_unqueue(list); from rcu_do_batch() is not finding 'list' in tracked objects.
I know that doing call_rcu() from trace_preempt is ill advised, but I still want to understand why call_rcu corrupts the memory.
Attaching a patch that I'm using for debugging. It's doing recursion preemption check, so number of nested call_rcu is no more than 2. Also if I replace kfree_rcu is this patch with a regular kfree, all works fine.
I'm seeing this crashes in VM with _single_ cpu. Kernel is built with CONFIG_PREEMPT, CONFIG_PREEMPT_TRACER and CONFIG_DEBUG_OBJECTS_RCU_HEAD.
Also interesting that size of struct elem { u64 pad[32]; struct rcu_head rcu; }; that I'm using in kmalloc/kfree_rcu changes the crash. If padding is zero, kernel just locksup, if pad[1] I see one type of odebug warnings, if pad[32] - another.
Any advise on where to look is greatly appreciated.
Thanks!
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c index 8523ea345f2b..89433a83dd2d 100644 --- a/kernel/trace/trace_irqsoff.c +++ b/kernel/trace/trace_irqsoff.c @@ -13,6 +13,7 @@ #include <linux/uaccess.h> #include <linux/module.h> #include <linux/ftrace.h> +#include <linux/slab.h> #include "trace.h" @@ -510,8 +511,42 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller); #endif /* CONFIG_IRQSOFF_TRACER */ #ifdef CONFIG_PREEMPT_TRACER +struct elem { + u64 pad[32]; + struct rcu_head rcu; +}; + +static DEFINE_PER_CPU(int, prog_active); +static void * test_alloc(void) +{ + struct elem *e = NULL; + + if (in_nmi()) + return e; + + preempt_disable_notrace(); + if (unlikely(__this_cpu_inc_return(prog_active) != 1)) + goto out; + + rcu_read_lock(); + e = kmalloc(sizeof(struct elem), GFP_ATOMIC); + rcu_read_unlock(); + if (!e) + goto out; + + kfree_rcu(e, rcu); +out: + __this_cpu_dec(prog_active); + preempt_enable_no_resched_notrace(); + return e; +} + void trace_preempt_on(unsigned long a0, unsigned long a1) { + void * buf = 0; + static int cnt = 0; + if (cnt++ > 3000000) + buf = test_alloc(); if (preempt_trace() && !irq_trace()) stop_critical_timing(a0, a1); } | |