On Tue, Jun 24, 2025 at 10:00:48PM +0800, David Wang wrote:
At 2025-06-24 21:50:02, "Harry Yoo" harry.yoo@oracle.com wrote:
On Tue, Jun 24, 2025 at 09:25:58PM +0800, David Wang wrote:
At 2025-06-24 15:25:13, "Harry Yoo" harry.yoo@oracle.com wrote:
alloc_tag_top_users() attempts to lock alloc_tag_cttype->mod_lock even when the alloc_tag_cttype is not allocated because:
- alloc tagging is disabled because mem profiling is disabled (!alloc_tag_cttype)
- alloc tagging is enabled, but not yet initialized (!alloc_tag_cttype)
- alloc tagging is enabled, but failed initialization (!alloc_tag_cttype or IS_ERR(alloc_tag_cttype))
In all cases, alloc_tag_cttype is not allocated, and therefore alloc_tag_top_users() should not attempt to acquire the semaphore.
This leads to a crash on memory allocation failure by attempting to acquire a non-existent semaphore:
Oops: general protection fault, probably for non-canonical address 0xdffffc000000001b: 0000 [#3] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x00000000000000d8-0x00000000000000df] CPU: 2 UID: 0 PID: 1 Comm: systemd Tainted: G D 6.16.0-rc2 #1 VOLUNTARY Tainted: [D]=DIE Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:down_read_trylock+0xaa/0x3b0 Code: d0 7c 08 84 d2 0f 85 a0 02 00 00 8b 0d df 31 dd 04 85 c9 75 29 48 b8 00 00 00 00 00 fc ff df 48 8d 6b 68 48 89 ea 48 c1 ea 03 <80> 3c 02 00 0f 85 88 02 00 00 48 3b 5b 68 0f 85 53 01 00 00 65 ff RSP: 0000:ffff8881002ce9b8 EFLAGS: 00010016 RAX: dffffc0000000000 RBX: 0000000000000070 RCX: 0000000000000000 RDX: 000000000000001b RSI: 000000000000000a RDI: 0000000000000070 RBP: 00000000000000d8 R08: 0000000000000001 R09: ffffed107dde49d1 R10: ffff8883eef24e8b R11: ffff8881002cec20 R12: 1ffff11020059d37 R13: 00000000003fff7b R14: ffff8881002cec20 R15: dffffc0000000000 FS: 00007f963f21d940(0000) GS:ffff888458ca6000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f963f5edf71 CR3: 000000010672c000 CR4: 0000000000350ef0 Call Trace:
<TASK> codetag_trylock_module_list+0xd/0x20 alloc_tag_top_users+0x369/0x4b0 __show_mem+0x1cd/0x6e0 warn_alloc+0x2b1/0x390 __alloc_frozen_pages_noprof+0x12b9/0x21a0 alloc_pages_mpol+0x135/0x3e0 alloc_slab_page+0x82/0xe0 new_slab+0x212/0x240 ___slab_alloc+0x82a/0xe00 </TASK>
As David Wang points out, this issue became easier to trigger after commit 780138b12381 ("alloc_tag: check mem_profiling_support in alloc_tag_init").
Before the commit, the issue occurred only when it failed to allocate and initialize alloc_tag_cttype or if a memory allocation fails before alloc_tag_init() is called. After the commit, it can be easily triggered when memory profiling is compiled but disabled at boot.
To properly determine whether alloc_tag_init() has been called and its data structures initialized, verify that alloc_tag_cttype is a valid pointer before acquiring the semaphore. If the variable is NULL or an error value, it has not been properly initialized. In such a case, just skip and do not attempt to acquire the semaphore.
Reported-by: kernel test robot oliver.sang@intel.com Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202506181351.bba8... Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-lkp/202506131711.5b41... Fixes: 780138b12381 ("alloc_tag: check mem_profiling_support in alloc_tag_init") Fixes: 1438d349d16b ("lib: add memory allocations report in show_mem()") Cc: stable@vger.kernel.org Signed-off-by: Harry Yoo harry.yoo@oracle.com
@Suren: I did not add another pr_warn() because every error path in alloc_tag_init() already has pr_err().
v2 -> v3:
- Added another Closes: tag (David)
- Moved the condition into a standalone if block for better readability
(Suren)
- Typo fix (Suren)
lib/alloc_tag.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index 41ccfb035b7b..e9b33848700a 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -127,6 +127,9 @@ size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sl struct codetag_bytes n; unsigned int i, nr = 0;
- if (IS_ERR_OR_NULL(alloc_tag_cttype))
return 0;What about mem_profiling_support set to 0 after alloc_tag_init, in this case: alloc_tag_cttype != NULL && mem_profiling_support==0
I kind of think alloc_tag_top_users should return 0 in this case....and both mem_profiling_support and alloc_tag_cttype should be checked....
After commit 780138b12381, alloc_tag_cttype is not allocated if !mem_profiling_support. (And that's why this bug showed up)
There is a sysctl(/proc/sys/vm/mem_profiling) which can override mem_profiling_support and set it to 0, after alloc_tag_init with mem_profiling_support=1
Ok. Maybe it shouldn't report memory allocation information that is collected before mem profiling was disabled. (I'm not sure why it disabling at runtime is allowed, though)
That's a good thing to have, but I think that's a behavioral change in mem profiling, irrelevant to this bug and not a -stable thing.
Maybe as a follow-up patch?
- if (can_sleep) codetag_lock_module_list(alloc_tag_cttype, true); else if (!codetag_trylock_module_list(alloc_tag_cttype))
-- 2.43.0
-- Cheers, Harry / Hyeonggon