Re: [PATCH v3 2/2] rcu: Dump vmalloc memory info safely

From: Lorenzo Stoakes <lstoakes@gmail.com>
To: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Zqiang <qiang.zhang1211@gmail.com>,
	Zhen Lei <thunder.leizhen@huaweicloud.com>,
	rcu@vger.kernel.org, Matthew Wilcox <willy@infradead.org>,
	stable@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 2/2] rcu: Dump vmalloc memory info safely
Date: Tue, 5 Sep 2023 08:00:44 +0100	[thread overview]
Message-ID: <9e329429-73a5-4926-af4f-edcf9e547101@lucifer.local> (raw)
In-Reply-To: <20230904180806.1002832-2-joel@joelfernandes.org>

On Mon, Sep 04, 2023 at 06:08:05PM +0000, Joel Fernandes (Google) wrote:
> From: Zqiang <qiang.zhang1211@gmail.com>
>
> Currently, for double invoke call_rcu(), will dump rcu_head objects
> memory info, if the objects is not allocated from the slab allocator,
> the vmalloc_dump_obj() will be invoke and the vmap_area_lock spinlock
> need to be held, since the call_rcu() can be invoked in interrupt context,
> therefore, there is a possibility of spinlock deadlock scenarios.
>
> And in Preempt-RT kernel, the rcutorture test also trigger the following
> lockdep warning:
>
> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
> preempt_count: 1, expected: 0
> RCU nest depth: 1, expected: 1
> 3 locks held by swapper/0/1:
>  #0: ffffffffb534ee80 (fullstop_mutex){+.+.}-{4:4}, at: torture_init_begin+0x24/0xa0
>  #1: ffffffffb5307940 (rcu_read_lock){....}-{1:3}, at: rcu_torture_init+0x1ec7/0x2370
>  #2: ffffffffb536af40 (vmap_area_lock){+.+.}-{3:3}, at: find_vmap_area+0x1f/0x70
> irq event stamp: 565512
> hardirqs last  enabled at (565511): [<ffffffffb379b138>] __call_rcu_common+0x218/0x940
> hardirqs last disabled at (565512): [<ffffffffb5804262>] rcu_torture_init+0x20b2/0x2370
> softirqs last  enabled at (399112): [<ffffffffb36b2586>] __local_bh_enable_ip+0x126/0x170
> softirqs last disabled at (399106): [<ffffffffb43fef59>] inet_register_protosw+0x9/0x1d0
> Preemption disabled at:
> [<ffffffffb58040c3>] rcu_torture_init+0x1f13/0x2370
> CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W          6.5.0-rc4-rt2-yocto-preempt-rt+ #15
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x68/0xb0
>  dump_stack+0x14/0x20
>  __might_resched+0x1aa/0x280
>  ? __pfx_rcu_torture_err_cb+0x10/0x10
>  rt_spin_lock+0x53/0x130
>  ? find_vmap_area+0x1f/0x70
>  find_vmap_area+0x1f/0x70
>  vmalloc_dump_obj+0x20/0x60
>  mem_dump_obj+0x22/0x90
>  __call_rcu_common+0x5bf/0x940
>  ? debug_smp_processor_id+0x1b/0x30
>  call_rcu_hurry+0x14/0x20
>  rcu_torture_init+0x1f82/0x2370
>  ? __pfx_rcu_torture_leak_cb+0x10/0x10
>  ? __pfx_rcu_torture_leak_cb+0x10/0x10
>  ? __pfx_rcu_torture_init+0x10/0x10
>  do_one_initcall+0x6c/0x300
>  ? debug_smp_processor_id+0x1b/0x30
>  kernel_init_freeable+0x2b9/0x540
>  ? __pfx_kernel_init+0x10/0x10
>  kernel_init+0x1f/0x150
>  ret_from_fork+0x40/0x50
>  ? __pfx_kernel_init+0x10/0x10
>  ret_from_fork_asm+0x1b/0x30
>  </TASK>
>
> The previous patch fixes this by using the deadlock-safe best-effort
> version of find_vm_area. However, in case of failure print the fact that
> the pointer was a vmalloc pointer so that we print at least something.
>
> Reported-by: Zhen Lei <thunder.leizhen@huaweicloud.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: rcu@vger.kernel.org
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Fixes: 98f180837a89 ("mm: Make mem_dump_obj() handle vmalloc() memory")
> Cc: stable@vger.kernel.org
> Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>  mm/util.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index dd12b9531ac4..406634f26918 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1071,7 +1071,9 @@ void mem_dump_obj(void *object)
>  	if (vmalloc_dump_obj(object))
>  		return;
>
> -	if (virt_addr_valid(object))
> +	if (is_vmalloc_addr(object))
> +		type = "vmalloc memory";
> +	else if (virt_addr_valid(object))
>  		type = "non-slab/vmalloc memory";

I think you should update this to say non-slab/non-vmalloc memory (as much
as that description sucks!) as this phrasing in the past meant to say
'non-slab or vmalloc memory' (already confusing phrasing) so better to be
clear.

>  	else if (object == NULL)
>  		type = "NULL pointer";
> --
> 2.42.0.283.g2d96d420d3-goog
>