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McKenney" To: "Zhang, Qiang1" Cc: "frederic@kernel.org" , "joel@joelfernandes.org" , "rcu@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] srcu: Fix flush sup work warning in cleanup_srcu_struct() Message-ID: Reply-To: paulmck@kernel.org References: <20230321081346.192000-1-qiang1.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 22, 2023 at 04:38:29AM +0000, Zhang, Qiang1 wrote: > > > insmod rcutorture.ko > > > rmmod rcutorture.ko > > > > > > [ 209.437327] WARNING: CPU: 0 PID: 508 at kernel/workqueue.c:3167 > > > __flush_work+0x50a/0x540 [ 209.437346] Modules linked in: > > > rcutorture(-) torture [last unloaded: rcutorture] [ 209.437382] > > > CPU: 0 PID: 508 Comm: rmmod Tainted: G W 6.3.0-rc1-yocto-standard+ > > > [ 209.437406] RIP: 0010:__flush_work+0x50a/0x540 ..... > > > [ 209.437758] flush_delayed_work+0x36/0x90 [ 209.437776] > > > cleanup_srcu_struct+0x68/0x2e0 [ 209.437817] > > > srcu_module_notify+0x71/0x140 [ 209.437854] > > > blocking_notifier_call_chain+0x9d/0xd0 > > > [ 209.437880] __x64_sys_delete_module+0x223/0x2e0 > > > [ 209.438046] do_syscall_64+0x43/0x90 [ 209.438062] > > > entry_SYSCALL_64_after_hwframe+0x72/0xdc > > > > > > For srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(), > > > when compiling and loading as modules, the srcu_module_coming() is > > > invoked, allocate memory for srcu structure's->sda and initialize > > > sda structure, due to not fully initialize srcu structure's->sup, so > > > at this time the sup structure's->delaywork.func is null, if not > > > invoke init_srcu_struct_fields() before unloading modules, in > > > srcu_module_going() the __flush_work() find > > > work->func is empty, will raise the warning above. > > > > > > This commit add init_srcu_struct_fields() to initialize srcu > > > structure's->sup, in srcu_module_coming(). > > > > > > Signed-off-by: Zqiang > > > > > >Good catch, and thank you for testing the in-module case! > > > > > >One question below... > > > > > > Thanx, Paul > > > > > > --- > > > kernel/rcu/srcutree.c | 11 ++++++++--- > > > 1 file changed, 8 insertions(+), 3 deletions(-) > > > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index > > > 1fb078abbdc9..42d8720e016c 100644 > > > --- a/kernel/rcu/srcutree.c > > > +++ b/kernel/rcu/srcutree.c > > > @@ -1921,7 +1921,8 @@ static int srcu_module_coming(struct module *mod) > > > ssp->sda = alloc_percpu(struct srcu_data); > > > if (WARN_ON_ONCE(!ssp->sda)) > > > return -ENOMEM; > > > - init_srcu_struct_data(ssp); > > > + if (WARN_ON_ONCE(init_srcu_struct_fields(ssp, true))) > > > + return -ENOMEM; > > > > > >Wouldn't it be better to simply delete the init_srcu_struct_data()? > > > > > >Then the first call to check_init_srcu_struct() would take care of > > >the initialization, just as for the non-module case. Or am I missing > > >something subtle? > > > > Hi Paul > > > > Maybe the check_init_srcu_struct() is always not invoked, for example, > > In rcutorture.c, here is such a definition DEFINE_STATIC_SRCU(srcu_ctl), > > but we use torture_type=rcu to test, there will not be any interface > > calling > > check_init_srcu_struct() to initialize srcu_ctl and set > > structure's->delaywork.func is process_srcu(). > > when we unload the rcutorture module, invoke cleanup_srcu_struct() to > > flush sup structure's->delaywork.func, due to the func pointer is not > > initialize, it's null, will trigger warning. > > > > About kernel/workqueue.c:3167 > > > > __flush_work > > if (WARN_ON(!work->func)) <---------trigger waning > > return false; > > > > > > and in init_srcu_struct_fields(ssp, true), wil set > > srcu_sup->sda_is_static is true and set srcu_sup-> srcu_gp_seq_needed > > is zero, after that when we call > > check_init_srcu_struct() again, it not be initialized again. > > > > > >Good point! In the non-module statically allocated case there is never a call to cleanup_srcu_struct(). > > > >So suppose the code in srcu_module_coming() only did the alloc_percpu(), and then the > >code in srcu_module_going() only did the the matching > >free_percpu() instead of the current cleanup_srcu_struct()? > > But in modules, for srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(), > when a module is unloaded, we usually don't call cleanup_srcu_struct() in the module > unload function. > If in srcu_module_going() only do free_percpu(), the srcu_sup->node memory maybe > can not free and also lost the opportunity to refresh the running work. But in the module case, isn't the srcu_sup->node also statically allocated via the "static struct srcu_usage" declaration? Thanx, Paul ------------------------------------------------------------------------ #ifdef MODULE # define __DEFINE_SRCU(name, is_static) \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ extern struct srcu_struct * const __srcu_struct_##name; \ struct srcu_struct * const __srcu_struct_##name \ __section("___srcu_struct_ptrs") = &name #else # define __DEFINE_SRCU(name, is_static) \ static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ is_static struct srcu_struct name = \ __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) #endif > Thanks > Zqiang > > > > > > Thanx, Paul > > > > Thanks > > Zqiang > > > > > > > >It should also be possible to eliminate duplicate code between the > > >in-module and non-module statically allocated initialization cases, > > >come to think of it. > > > > > > } > > > return 0; > > > } > > > @@ -1931,9 +1932,13 @@ static void srcu_module_going(struct module > > > *mod) { > > > int i; > > > struct srcu_struct **sspp = mod->srcu_struct_ptrs; > > > + struct srcu_struct *ssp; > > > > > > - for (i = 0; i < mod->num_srcu_structs; i++) > > > - cleanup_srcu_struct(*(sspp++)); > > > + for (i = 0; i < mod->num_srcu_structs; i++) { > > > + ssp = *(sspp++); > > > + cleanup_srcu_struct(ssp); > > > + free_percpu(ssp->sda); > > > + } > > > > > >And good catch on another memory leak with this one, looks proper to > > >me. > > > > > > } > > > > > > /* Handle one module, either coming or going. */ > > > -- > > > 2.25.1 > > >