On Thu, Sep 07, 2023 at 09:10:38AM +0200, Vlastimil Babka wrote:
On 9/6/23 21:18, Lorenzo Stoakes wrote:
On Tue, 5 Sept 2023 at 12:48, Joel Fernandes joel@joelfernandes.org wrote:
On Tue, Sep 05, 2023 at 08:00:44AM +0100, Lorenzo Stoakes wrote:
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.
True, though the issue you mentioned it is in existing code, a respin of this patch could update it to say non-vmalloc. Good point, thanks for reviewing!
No it's not, you're changing the meaning, because you changed the code that determines the output...
I think it has always meant (but clearly it's not unambiguously worded) "not slab && not vmalloc", that is before and after this patch. Only in case patch 1 is applied and patch 2 not, can the output be wrong in that a vmalloc pointer will (in case of trylock fail) be classified as "not slab && not vmalloc", but seems fine to me after patch 2.
I guess if we wanted, we could also rewrite it to be more like the kmem check in the beginning of mem_dump_obj(), so there would be:
if (is_vmalloc_addr(...)) { vmalloc_dump_obj(...); return; }
where vmalloc_dump_obj() itself would print at least "vmalloc memory" with no further details in case of trylock failure.
that assumes is_vmalloc_addr() is guaranteed to be true for all addresses that __find_vmap_area resolves, otherwise it could miss something compared to current code. Is it guaranteed?
It is guaranteed based on my reading of the code. But maybe it may aid additional vmalloc-internals debugging if for some reason the address of the object stored in the vmalloc data structures is out of bound for some reason and the lookup actually succeded. That's just a hypothetical situation though and I don't think that that can actually happen.
thanks,
- Joel