Re: CONFIG_TEST_VMALLOC=y conflict/race with alloc_tag_init

["David Wang" <00107082@163.com>]

At 2025-06-23 19:36:03, "Uladzislau Rezki" <urezki@gmail.com> wrote:
>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 :)

Yes,   strangely lucky here~ :)
I was thinking, if some vmalloc tests fail, is alloc_tag_top_users helpful for debug?
Considering this bug has already been caught,  if alloc_tag_top_users is helpful for vmalloc test analysis,
maybe it is still reasonable to delay vmalloc_test_init?... ☺︎

>
>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