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McKenney" , rcu@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/2] rcu: Dump vmalloc memory info safely Message-ID: References: <20230830110402.386898-1-joel@joelfernandes.org> <20230830110402.386898-2-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230830110402.386898-2-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 30, 2023 at 11:04:00AM +0000, Joel Fernandes (Google) wrote: > From: Zqiang > > 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): [] __call_rcu_common+0x218/0x940 > hardirqs last disabled at (565512): [] rcu_torture_init+0x20b2/0x2370 > softirqs last enabled at (399112): [] __local_bh_enable_ip+0x126/0x170 > softirqs last disabled at (399106): [] inet_register_protosw+0x9/0x1d0 > Preemption disabled at: > [] 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: > > 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 > > > 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 > Cc: Paul E. McKenney > Cc: rcu@vger.kernel.org > Signed-off-by: Zqiang > Signed-off-by: Joel Fernandes (Google) Reviewed-by: Matthew Wilcox (Oracle)