Re: [PATCH v2] rcu: Dump memory object info if callback function is invalid

From: Paul E. McKenney
Date: Sat Nov 12 2022 - 01:09:14 EST

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On Sat, Nov 12, 2022 at 10:39:55AM +0800, Leizhen (ThunderTown) wrote:
> On 2022/11/12 10:32, Leizhen (ThunderTown) wrote:
> > On 2022/11/12 2:42, Paul E. McKenney wrote:
> >> On Fri, Nov 11, 2022 at 01:05:56PM +0000, Zhang, Qiang1 wrote:
> >>> On 2022/11/11 19:54, Zhang, Qiang1 wrote:
> >>>>> When a structure containing an RCU callback rhp is (incorrectly)
> >>>>> freed and reallocated after rhp is passed to call_rcu(), it is not
> >>>>> unusual for
> >>>>> rhp->func to be set to NULL. This defeats the debugging prints used
> >>>>> rhp->by
> >>>>> __call_rcu_common() in kernels built with
> >>>>> CONFIG_DEBUG_OBJECTS_RCU_HEAD=y, which expect to identify the
> >>>>> offending code using the identity of this function.
> >>>>>
> >>>>> And in kernels build without CONFIG_DEBUG_OBJECTS_RCU_HEAD=y, things
> >>>>> are even worse, as can be seen from this splat:
> >>>>>
> >>>>> Unable to handle kernel NULL pointer dereference at virtual address 0
> >>>>> ... ...
> >>>>> PC is at 0x0
> >>>>> LR is at rcu_do_batch+0x1c0/0x3b8
> >>>>> ... ...
> >>>>> (rcu_do_batch) from (rcu_core+0x1d4/0x284)
> >>>>> (rcu_core) from (__do_softirq+0x24c/0x344)
> >>>>> (__do_softirq) from (__irq_exit_rcu+0x64/0x108)
> >>>>> (__irq_exit_rcu) from (irq_exit+0x8/0x10)
> >>>>> (irq_exit) from (__handle_domain_irq+0x74/0x9c)
> >>>>> (__handle_domain_irq) from (gic_handle_irq+0x8c/0x98)
> >>>>> (gic_handle_irq) from (__irq_svc+0x5c/0x94)
> >>>>> (__irq_svc) from (arch_cpu_idle+0x20/0x3c)
> >>>>> (arch_cpu_idle) from (default_idle_call+0x4c/0x78)
> >>>>> (default_idle_call) from (do_idle+0xf8/0x150)
> >>>>> (do_idle) from (cpu_startup_entry+0x18/0x20)
> >>>>> (cpu_startup_entry) from (0xc01530)
> >>>>>
> >>>>> This commit therefore adds calls to mem_dump_obj(rhp) to output some
> >>>>> information, for example:
> >>>>>
> >>>>> slab kmalloc-256 start ffff410c45019900 pointer offset 0 size 256
> >>>>>
> >>>>> This provides the rough size of the memory block and the offset of
> >>>>> the rcu_head structure, which as least provides at least a few clues
> >>>>> to help locate the problem. If the problem is reproducible,
> >>>>> additional slab debugging can be enabled, for example,
> >>>>> CONFIG_DEBUG_SLAB=y, which can provide significantly more information.
> >>>>>
> >>>>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
> >>>>> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> >>>>> ---
> >>>>> kernel/rcu/rcu.h | 7 +++++++
> >>>>> kernel/rcu/srcutiny.c | 1 +
> >>>>> kernel/rcu/srcutree.c | 1 +
> >>>>> kernel/rcu/tasks.h | 1 +
> >>>>> kernel/rcu/tiny.c | 1 +
> >>>>> kernel/rcu/tree.c | 1 +
> >>>>> 6 files changed, 12 insertions(+)
> >>>>>
> >>>>> v1 --> v2:
> >>>>> 1. Remove condition "(unsigned long)rhp->func & 0x3", it have problems on x86.
> >>>>> 2. Paul E. McKenney helped me update the commit message, thanks.
> >>>>>
> >>>>
> >>>> Hi, Zhen Lei
> >>>>
> >>>> Maybe the following scenarios should be considered:
> >>>>
> >>>> CPU 0
> >>>> tasks context
> >>>> spin_lock(&vmap_area_lock)
> >>>> Interrupt
> >>>> RCU softirq
> >>>> rcu_do_batch
> >>>> mem_dump_obj
> >>>> vmalloc_dump_obj
> >>>> spin_lock(&vmap_area_lock) <-- deadlock
> >>>
> >>>> Right, thanks. I just saw the robot's report. So this patch should be dropped.
> >>>> I'll try to add an helper in mm, where I can check whether the lock has been held, and dump the content of memory object.
> >>>
> >>> This is a workaround, or maybe try a modification like the following,
> >>> of course, need to ask Paul's opinion.
> >>
> >> Another approach is to schedule a workqueue handler to do the
> >> mem_dump_obj(). This would allow mem_dump_obj() to run in a clean
> >> environment.
> >
> > It's about to panic, so no chance to schedule.
> >
> >>
> >> This would allow vmalloc_dump_obj() to be called unconditionally.
> >>
> >> Other thoughts?
> >
> > locked = spin_is_locked(&vmap_area_lock);
> > if (!locked)
> > spin_lock(&vmap_area_lock)
> >
> > Careful analysis is required, which may cause other problems.
> >
> > Or in new function:
>
> Oh, perhaps no new function is needed, mem_dump_obj() itself prints
> debugging information. I will try a mm patch first.

That does sound very worth trying!

Thanx, Paul

> > if (locked)
> > return;
> > spin_lock(&vmap_area_lock);
> >
> > If there is a chance to dump the data, dump the data. If there is no
> > chance to dump the data, do not dump the data. This is the fate of
> > debugging information.
> >
> >>
> >> Thanx, Paul
> >>
> >>> diff --git a/mm/util.c b/mm/util.c
> >>> index 12984e76767e..86da0739fe5d 100644
> >>> --- a/mm/util.c
> >>> +++ b/mm/util.c
> >>> @@ -1119,14 +1119,18 @@ void mem_dump_obj(void *object)
> >>> {
> >>> const char *type;
> >>>
> >>> + if (is_vmalloc_addr(object)) {
> >>> + if (in_task() && vmalloc_dump_obj(object))
> >>> + return;
> >>> + type = "vmalloc memory";
> >>> + goto end;
> >>> + }
> >>> +
> >>> if (kmem_valid_obj(object)) {
> >>> kmem_dump_obj(object);
> >>> return;
> >>> }
> >>>
> >>> - if (vmalloc_dump_obj(object))
> >>> - return;
> >>> -
> >>> if (virt_addr_valid(object))
> >>> type = "non-slab/vmalloc memory";
> >>> else if (object == NULL)
> >>> @@ -1135,7 +1139,7 @@ void mem_dump_obj(void *object)
> >>> type = "zero-size pointer";
> >>> else
> >>> type = "non-paged memory";
> >>> -
> >>> +end:
> >>> pr_cont(" %s\n", type);
> >>> }
> >>> EXPORT_SYMBOL_GPL(mem_dump_obj);
> >>>
> >>> Thanks
> >>> Zqiang
> >>>
> >>>
> >>>>
> >>>> Thanks
> >>>> Zqiang
> >>>>
> >>>>
> >>>>> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index
> >>>>> 65704cbc9df7b3d..32ab45fabf8eebf 100644
> >>>>> --- a/kernel/rcu/rcu.h
> >>>>> +++ b/kernel/rcu/rcu.h
> >>>>> @@ -10,6 +10,7 @@
> >>>>> #ifndef __LINUX_RCU_H
> >>>>> #define __LINUX_RCU_H
> >>>>>
> >>>>> +#include <linux/mm.h>
> >>>>> #include <trace/events/rcu.h>
> >>>>>
> >>>>> /*
> >>>>> @@ -211,6 +212,12 @@ static inline void debug_rcu_head_unqueue(struct
> >>>>> rcu_head *head) }
> >>>>> #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> >>>>>
> >>>>> +static inline void debug_rcu_head_callback(struct rcu_head *rhp) {
> >>>>> + if (unlikely(!rhp->func))
> >>>>> + mem_dump_obj(rhp);
> >>>>> +}
> >>>>> +
> >>>>> extern int rcu_cpu_stall_suppress_at_boot;
> >>>>>
> >>>>> static inline bool rcu_stall_is_suppressed_at_boot(void)
> >>>>> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index
> >>>>> 33adafdad261389..5e7f336baa06ae0 100644
> >>>>> --- a/kernel/rcu/srcutiny.c
> >>>>> +++ b/kernel/rcu/srcutiny.c
> >>>>> @@ -138,6 +138,7 @@ void srcu_drive_gp(struct work_struct *wp)
> >>>>> while (lh) {
> >>>>> rhp = lh;
> >>>>> lh = lh->next;
> >>>>> + debug_rcu_head_callback(rhp);
> >>>>> local_bh_disable();
> >>>>> rhp->func(rhp);
> >>>>> local_bh_enable();
> >>>>> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index
> >>>>> ca4b5dcec675bac..294972e66b31863 100644
> >>>>> --- a/kernel/rcu/srcutree.c
> >>>>> +++ b/kernel/rcu/srcutree.c
> >>>>> @@ -1631,6 +1631,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
> >>>>> rhp = rcu_cblist_dequeue(&ready_cbs);
> >>>>> for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
> >>>>> debug_rcu_head_unqueue(rhp);
> >>>>> + debug_rcu_head_callback(rhp);
> >>>>> local_bh_disable();
> >>>>> rhp->func(rhp);
> >>>>> local_bh_enable();
> >>>>> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index
> >>>>> b0b885e071fa8dc..b7f8c67c586cdc4 100644
> >>>>> --- a/kernel/rcu/tasks.h
> >>>>> +++ b/kernel/rcu/tasks.h
> >>>>> @@ -478,6 +478,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
> >>>>> raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
> >>>>> len = rcl.len;
> >>>>> for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp =
> >>>>> rcu_cblist_dequeue(&rcl)) {
> >>>>> + debug_rcu_head_callback(rhp);
> >>>>> local_bh_disable();
> >>>>> rhp->func(rhp);
> >>>>> local_bh_enable();
> >>>>> diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index
> >>>>> bb8f7d270f01747..56e9a5d91d97ec5 100644
> >>>>> --- a/kernel/rcu/tiny.c
> >>>>> +++ b/kernel/rcu/tiny.c
> >>>>> @@ -97,6 +97,7 @@ static inline bool rcu_reclaim_tiny(struct rcu_head
> >>>>> *head)
> >>>>>
> >>>>> trace_rcu_invoke_callback("", head);
> >>>>> f = head->func;
> >>>>> + debug_rcu_head_callback(head);
> >>>>> WRITE_ONCE(head->func, (rcu_callback_t)0L);
> >>>>> f(head);
> >>>>> rcu_lock_release(&rcu_callback_map);
> >>>>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index
> >>>>> 15aaff3203bf2d0..ed93ddb8203d42c 100644
> >>>>> --- a/kernel/rcu/tree.c
> >>>>> +++ b/kernel/rcu/tree.c
> >>>>> @@ -2088,6 +2088,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
> >>>>> trace_rcu_invoke_callback(rcu_state.name, rhp);
> >>>>>
> >>>>> f = rhp->func;
> >>>>> + debug_rcu_head_callback(rhp);
> >>>>> WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
> >>>>> f(rhp);
> >>>>>
> >>>>> --
> >>>>> 2.25.1
> >>>>
> >>>> .
> >>>>
> >>>
> >>> --
> >>> Regards,
> >>> Zhen Lei
> >> .
> >>
> >
>
> --
> Regards,
> Zhen Lei

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Previous message: Paul E. McKenney: "Re: [PATCH v2] rcu: Dump memory object info if callback function is invalid"
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