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PH7PR12MB7161.namprd12.prod.outlook.com (2603:10b6:510:200::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8813.38; Mon, 30 Jun 2025 06:25:14 +0000 Received: from PH7PR12MB5805.namprd12.prod.outlook.com ([fe80::11c7:4914:62f4:f4a3]) by PH7PR12MB5805.namprd12.prod.outlook.com ([fe80::11c7:4914:62f4:f4a3%4]) with mapi id 15.20.8857.026; Mon, 30 Jun 2025 06:25:14 +0000 Message-ID: <491a68b9-a2ca-4ca8-8d36-5775762088cd@amd.com> Date: Mon, 30 Jun 2025 11:55:06 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] lib/alloc_tag: do not acquire non-existent lock in alloc_tag_top_users() To: Harry Yoo , akpm@linux-foundation.org, surenb@google.com, kent.overstreet@linux.dev Cc: oliver.sang@intel.com, 00107082@163.com, cachen@purestorage.com, linux-mm@kvack.org, oe-lkp@lists.linux.dev, stable@vger.kernel.org References: <20250624072513.84219-1-harry.yoo@oracle.com> Content-Language: en-US From: Raghavendra K T In-Reply-To: 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6/24/2025 12:55 PM, Harry Yoo wrote: > alloc_tag_top_users() attempts to lock alloc_tag_cttype->mod_lock > even when the alloc_tag_cttype is not allocated because: > > 1) alloc tagging is disabled because mem profiling is disabled > (!alloc_tag_cttype) > 2) alloc tagging is enabled, but not yet initialized (!alloc_tag_cttype) > 3) 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: > > 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 > > > 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 > Closes: https://lore.kernel.org/oe-lkp/202506181351.bba867dd-lkp@intel.com > Closes: https://lore.kernel.org/oe-lkp/202506131711.5b41931c-lkp@intel.com > 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 > --- > > @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; > + > if (can_sleep) > codetag_lock_module_list(alloc_tag_cttype, true); > else if (!codetag_trylock_module_list(alloc_tag_cttype)) Hello, I have hit this while digging one of the TEST_VMALLOC test. (specifically align_shift_alloc_test which is expected to fail and give similar splat) I can confirm that with CONFIG_MEM_ALLOC_PROFILING=y CONFIG_TEST_VMALLOC=y system does not boot (for v6.16+). with this patch system boots fine. and thus seems to be a mandatory fix. (for the above CONFIG combination) Fell free to add: Tested-by: Raghavendra K T Thanks and Regards - Raghu