Re: CONFIG_TEST_VMALLOC=y conflict/race with alloc_tag_init

[Uladzislau Rezki <urezki@gmail.com>]

On Mon, Jun 23, 2025 at 10:45:31AM +0800, David Wang wrote:
> 
> At 2025-06-23 06:50:44, "Suren Baghdasaryan" <surenb@google.com> wrote:
> >On Fri, Jun 20, 2025 at 3:03 AM David Wang <00107082@163.com> wrote:
> >>
> >> On Wed, Jun 18, 2025 at 02:25:37PM +0800, kernel test robot wrote:
> >> >
> >> > Hello,
> >> >
> >> > for this change, we reported
> >> > "[linux-next:master] [lib/test_vmalloc.c]  7fc85b92db: Mem-Info"
> >> > in
> >> > https://lore.kernel.org/all/202505071555.e757f1e0-lkp@intel.com/
> >> >
> >> > at that time, we made some tests with x86_64 config which runs well.
> >> >
> >> > now we noticed the commit is in mainline now.
> >>
> >> > the config still has expected diff with parent:
> >> >
> >> > --- /pkg/linux/x86_64-randconfig-161-20250614/gcc-12/7a73348e5d4715b5565a53f21c01ea7b54e46cbd/.config   2025-06-17 14:40:29.481052101 +0800
> >> > +++ /pkg/linux/x86_64-randconfig-161-20250614/gcc-12/2d76e79315e403aab595d4c8830b7a46c19f0f3b/.config   2025-06-17 14:41:18.448543738 +0800
> >> > @@ -7551,7 +7551,7 @@ CONFIG_TEST_IDA=m
> >> >  CONFIG_TEST_MISC_MINOR=m
> >> >  # CONFIG_TEST_LKM is not set
> >> >  CONFIG_TEST_BITOPS=m
> >> > -CONFIG_TEST_VMALLOC=m
> >> > +CONFIG_TEST_VMALLOC=y
> >> >  # CONFIG_TEST_BPF is not set
> >> >  CONFIG_FIND_BIT_BENCHMARK=m
> >> >  # CONFIG_TEST_FIRMWARE is not set
> >> >
> >> >
> >> > then we noticed similar random issue with x86_64 randconfig this time.
> >> >
> >> > 7a73348e5d4715b5 2d76e79315e403aab595d4c8830
> >> > ---------------- ---------------------------
> >> >        fail:runs  %reproduction    fail:runs
> >> >            |             |             |
> >> >            :199         34%          67:200   dmesg.KASAN:null-ptr-deref_in_range[#-#]
> >> >            :199         34%          67:200   dmesg.Kernel_panic-not_syncing:Fatal_exception
> >> >            :199         34%          67:200   dmesg.Mem-Info
> >> >            :199         34%          67:200   dmesg.Oops:general_protection_fault,probably_for_non-canonical_address#:#[##]SMP_KASAN
> >> >            :199         34%          67:200   dmesg.RIP:down_read_trylock
> >> >
> >> > we don't have enough knowledge to understand the relationship between code
> >> > change and the random issues. just report what we obsverved in our tests FYI.
> >> >
> >>
> >> I think this is caused by a race between vmalloc_test_init and alloc_tag_init.
> >>
> >> vmalloc_test actually depends on alloc_tag via alloc_tag_top_users, because when
> >> memory allocation fails show_mem() would invoke alloc_tag_top_users.
> >>
> >> With following configuration:
> >>
> >> CONFIG_TEST_VMALLOC=y
> >> CONFIG_MEM_ALLOC_PROFILING=y
> >> CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y
> >> CONFIG_MEM_ALLOC_PROFILING_DEBUG=y
> >>
> >> If vmalloc_test_init starts before alloc_tag_init, show_mem() would cause
> >> a NULL deference because alloc_tag_cttype was not init yet.
> >>
> >> I add some debug to confirm this theory
> >> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> >> index d48b80f3f007..9b8e7501010f 100644
> >> --- a/lib/alloc_tag.c
> >> +++ b/lib/alloc_tag.c
> >> @@ -133,6 +133,8 @@ size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sl
> >>         struct codetag *ct;
> >>         struct codetag_bytes n;
> >>         unsigned int i, nr = 0;
> >> +       pr_info("memory profiling alloc top %d: %llx\n", mem_profiling_support, (long long)alloc_tag_cttype);
> >> +       return 0;
> >>
> >>         if (can_sleep)
> >>                 codetag_lock_module_list(alloc_tag_cttype, true);
> >> @@ -831,6 +833,7 @@ static int __init alloc_tag_init(void)
> >>                 shutdown_mem_profiling(true);
> >>                 return PTR_ERR(alloc_tag_cttype);
> >>         }
> >> +       pr_info("memory profiling ready %d: %llx\n", mem_profiling_support, (long long)alloc_tag_cttype);
> >>
> >>         return 0;
> >>  }
> >>
> >> When bootup the kernel, the log shows:
> >>
> >> $ sudo dmesg -T | grep profiling
> >> [Fri Jun 20 17:29:35 2025] memory profiling alloc top 1: 0  <--- alloc_tag_cttype == NULL
> >> [Fri Jun 20 17:30:24 2025] memory profiling ready 1: ffff9b1641aa06c0
> >>
> >>
> >> vmalloc_test_init should happened after alloc_tag_init if CONFIG_TEST_VMALLOC=y,
> >> or mem_show() should check whether alloc_tag is done initialized when calling
> >> alloc_tag_top_users
> >
> >Thanks for reporting!
> >So, IIUC https://lore.kernel.org/all/20250620195305.1115151-1-harry.yoo@oracle.com/
> >will address this issue as well. Is that correct?
> 
> Yes, the panic can be fix by that patch.
> 
> I still feel it better to delay vmalloc_test_init, make it happen after alloc_tag_init.
>
We can, but then we would not notice the bag that is in question :)

At least we should, i think, to exclude the tests which trigger warnings
when the test-suite is run with default configurations, i.e. run the tests
which are not supposed to fail.

--
Uladzislau Rezki