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

[Uladzislau Rezki]

>
> 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@xxxxxxxxxxxxx>
> > Signed-off-by: Jun Miao <jun.miao@xxxxxxxxxxxxx>
> > ---
> >   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