Re: [PATCH] rcu: avoid alloc_pages() when recording stack

["Paul E. McKenney" <paulmck@kernel.org>]

On Thu, Nov 04, 2021 at 09:09:24AM +0800, Jun Miao wrote:
> 
> On 11/4/21 5:21 AM, Paul E. McKenney wrote:
> > [Please note: This e-mail is from an EXTERNAL e-mail address]
> > 
> > On Wed, Nov 03, 2021 at 11:13:15AM -0700, Paul E. McKenney wrote:
> > > On Wed, Nov 03, 2021 at 02:55:48PM +0100, Uladzislau Rezki wrote:
> > > > On Wed, Nov 3, 2021 at 7:51 AM Jun Miao <jun.miao@windriver.com> wrote:
> > > > > 
> > > > > On 11/2/21 10:53 PM, Uladzislau Rezki wrote:
> > > > > > [Please note: This e-mail is from an EXTERNAL e-mail address]
> > > > > > 
> > > > > > > Add KASAN maintainers
> > > > > > > 
> > > > > > > On 11/1/21 6:31 PM, Jun Miao wrote:
> > > > > > > > The default kasan_record_aux_stack() calls stack_depot_save() with GFP_NOWAIT,
> > > > > > > > which in turn can then call alloc_pages(GFP_NOWAIT, ...).  In general, however,
> > > > > > > > it is not even possible to use either GFP_ATOMIC nor GFP_NOWAIT in certain
> > > > > > > > non-preemptive contexts/RT kernel including raw_spin_locks (see gfp.h and ab00db216c9c7).
> > > > > > > > 
> > > > > > > > Fix it by instructing stackdepot to not expand stack storage via alloc_pages()
> > > > > > > > in case it runs out by using kasan_record_aux_stack_noalloc().
> > > > > > > > 
> > > > > > > > Jianwei Hu reported:
> > > > > > > >     BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:969
> > > > > > > >     in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 15319, name: python3
> > > > > > > >     INFO: lockdep is turned off.
> > > > > > > >     irq event stamp: 0
> > > > > > > >     hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> > > > > > > >     hardirqs last disabled at (0): [<ffffffff856c8b13>] copy_process+0xaf3/0x2590
> > > > > > > >     softirqs last  enabled at (0): [<ffffffff856c8b13>] copy_process+0xaf3/0x2590
> > > > > > > >     softirqs last disabled at (0): [<0000000000000000>] 0x0
> > > > > > > >     CPU: 6 PID: 15319 Comm: python3 Tainted: G        W  O 5.15-rc7-preempt-rt #1
> > > > > > > >     Hardware name: Supermicro SYS-E300-9A-8C/A2SDi-8C-HLN4F, BIOS 1.1b 12/17/2018
> > > > > > > >     Call Trace:
> > > > > > > >      show_stack+0x52/0x58
> > > > > > > >      dump_stack+0xa1/0xd6
> > > > > > > >      ___might_sleep.cold+0x11c/0x12d
> > > > > > > >      rt_spin_lock+0x3f/0xc0
> > > > > > > >      rmqueue+0x100/0x1460
> > > > > > > >      rmqueue+0x100/0x1460
> > > > > > > >      mark_usage+0x1a0/0x1a0
> > > > > > > >      ftrace_graph_ret_addr+0x2a/0xb0
> > > > > > > >      rmqueue_pcplist.constprop.0+0x6a0/0x6a0
> > > > > > > >       __kasan_check_read+0x11/0x20
> > > > > > > >       __zone_watermark_ok+0x114/0x270
> > > > > > > >       get_page_from_freelist+0x148/0x630
> > > > > > > >       is_module_text_address+0x32/0xa0
> > > > > > > >       __alloc_pages_nodemask+0x2f6/0x790
> > > > > > > >       __alloc_pages_slowpath.constprop.0+0x12d0/0x12d0
> > > > > > > >       create_prof_cpu_mask+0x30/0x30
> > > > > > > >       alloc_pages_current+0xb1/0x150
> > > > > > > >       stack_depot_save+0x39f/0x490
> > > > > > > >       kasan_save_stack+0x42/0x50
> > > > > > > >       kasan_save_stack+0x23/0x50
> > > > > > > >       kasan_record_aux_stack+0xa9/0xc0
> > > > > > > >       __call_rcu+0xff/0x9c0
> > > > > > > >       call_rcu+0xe/0x10
> > > > > > > >       put_object+0x53/0x70
> > > > > > > >       __delete_object+0x7b/0x90
> > > > > > > >       kmemleak_free+0x46/0x70
> > > > > > > >       slab_free_freelist_hook+0xb4/0x160
> > > > > > > >       kfree+0xe5/0x420
> > > > > > > >       kfree_const+0x17/0x30
> > > > > > > >       kobject_cleanup+0xaa/0x230
> > > > > > > >       kobject_put+0x76/0x90
> > > > > > > >       netdev_queue_update_kobjects+0x17d/0x1f0
> > > > > > > >       ... ...
> > > > > > > >       ksys_write+0xd9/0x180
> > > > > > > >       __x64_sys_write+0x42/0x50
> > > > > > > >       do_syscall_64+0x38/0x50
> > > > > > > >       entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > > > > > > 
> > > > > > > > Fixes: 84109ab58590 ("rcu: Record kvfree_call_rcu() call stack for KASAN")
> > > > > > > > Fixes: 26e760c9a7c8 ("rcu: kasan: record and print call_rcu() call stack")
> > > > > > > > Reported-by: Jianwei Hu <jianwei.hu@windriver.com>
> > > > > > > > Signed-off-by: Jun Miao <jun.miao@windriver.com>
> > > > > > > > ---
> > > > > > > >     kernel/rcu/tree.c | 4 ++--
> > > > > > > >     1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > > 
> > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > > > > > > index 8270e58cd0f3..2c1034580f15 100644
> > > > > > > > --- a/kernel/rcu/tree.c
> > > > > > > > +++ b/kernel/rcu/tree.c
> > > > > > > > @@ -3026,7 +3026,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > > > > > >         head->func = func;
> > > > > > > >         head->next = NULL;
> > > > > > > >         local_irq_save(flags);
> > > > > > > > -     kasan_record_aux_stack(head);
> > > > > > > > +     kasan_record_aux_stack_noalloc(head);
> > > > > > > >         rdp = this_cpu_ptr(&rcu_data);
> > > > > > > > 
> > > > > > > >         /* Add the callback to our list. */
> > > > > > > > @@ -3591,7 +3591,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > > > > > >                 return;
> > > > > > > >         }
> > > > > > > > 
> > > > > > > > -     kasan_record_aux_stack(ptr);
> > > > > > > > +     kasan_record_aux_stack_noalloc(ptr);
> > > > > > > >         success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
> > > > > > > >         if (!success) {
> > > > > > > >                 run_page_cache_worker(krcp);
> > > > > > Yep an allocation is tricky here. This change looks correct to me at
> > > > > > least from the point that it does not allocate.
> > > > > > 
> > > > > > --
> > > > > > Uladzislau Rezki
> > > > > Thanks your approval. Could you like to give me a review?
> > > > > 
> > > > Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > > I have queued it for review and testing, thank you both!  I do have
> > > some remaining concerns about this code being starved for memory.  I am
> > > wondering if the code needs to check the interrupt state.  And perhaps
> > > also whether locks are held.  I of course will refrain from sending
> > > this to mainline until these concerns are resolved.
> > > 
> > > Marco, Dmitry, thoughts?
> > Well, the compiler does have an opinion:
> > 
> > kernel/rcu/tree.c: In function ‘__call_rcu’:
> > kernel/rcu/tree.c:3029:2: error: implicit declaration of function ‘kasan_record_aux_stack_noalloc’; did you mean ‘kasan_record_aux_stack’? [-Werror=implicit-function-declaration]
> >   3029 |  kasan_record_aux_stack_noalloc(head);
> >        |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >        |  kasan_record_aux_stack
> > 
> > I get the same message after merging in current mainline.
> > 
> > I have therefore dropped this patch for the time being.
> > 
> >                                                          Thanx, Paul
> Hi Paul E,
> The kasan_record_aux_stack_noalloc() is just introduce to linux-next now,
> and marking "Notice: this object is not reachable from any branch." in
> commit.
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/include/linux/kasan.h?h=next-20211029&id=2f64acf6b653d01fbdc92a693f12bbf71a205926

That would explain it!  Feel free to resend once the functionality is
more generally available.

							Thanx, Paul