On Mon, Sep 04, 2023 at 06:08:05PM +0000, Joel Fernandes (Google) wrote:
> From: Zqiang <qiang.zhang1211@xxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: rcu@xxxxxxxxxxxxxxx
> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Fixes: 98f180837a89 ("mm: Make mem_dump_obj() handle vmalloc() memory")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> 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
>
