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Fri, 18 Sep 2026 01:38:20 +0000 X-Mizu-Trace-ID: 9f10f04cf85e3f6a X-Migadu-Flow: FLOW_OUT Message-ID: Date: Fri, 18 Sep 2026 09:39:12 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 6/6] alloc_tag: Defer /proc/allocinfo removal to a workqueue To: Suren Baghdasaryan Cc: Luis Chamberlain , Petr Pavlu , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Kent Overstreet , Andrew Morton , linux-modules@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko , stable@vger.kernel.org References: <20260915070001.113559-1-hao.ge@linux.dev> <20260915070001.113559-7-hao.ge@linux.dev> Content-Language: en-US From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 82D4520003 X-Stat-Signature: rhmqydjz81idsdrh3ungz79wx5fszpgw X-HE-Tag: 1789695501-648599 X-HE-Meta: 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 orxNPHA0 uu+l2Z08FSybpAKFGHCXCqV5Fusz8c/RiRqtUWhkogG4ngxij42zWW/7oOWglGVaCnfa/CjqkTzTsYpjgeediLo14BLcERO238tBRaIzBtr2r6rvy4KCC55igBbvVpvUc6h0ufM4+1i6hS4Ij6joFJCOaJBgcNbTzpbC6FC7wego++8KHrlAOvyHH8D17FT+aDBluAT/qmEK2RMmCDfq1RWvwOypAm3hVd7LwI9LGb5na4hA2B9EMJ/hQaE2YpZt8x9GtPU+uCGFrE7wPtpRUfnpLjDKBKcbMXVzSF2xK6fIAAjmQ2sBS6FYrMPfeTejzoWrOA8ciqOWmB7iCttJ3qOU3EcX8TUdGfuXWrlVwhqB2hf0SwuBM3ugNtA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Suren On 2026/9/18 09:09, Suren Baghdasaryan wrote: > On Mon, Sep 14, 2026 at 11:59 PM Hao Ge wrote: >> >> shutdown_mem_profiling() calls remove_proc_entry() from >> reserve_module_tags(), which runs under mod_lock held for write. >> remove_proc_entry() waits for readers, and a reader takes mod_lock for >> read in allocinfo_start(): >> >> CPU0 (insmod) CPU1 (read /proc/allocinfo) >> ---------------- ---------------------------- >> reserve_module_tags() >> down_write(&mod_lock) [held] >> use_pde() [in_use++] >> allocinfo_start() >> down_read(&mod_lock) <- blocks >> shutdown_mem_profiling() >> remove_proc_entry() >> wait for in_use == 0 <- blocks >> >> Move remove_proc_entry() to a workqueue. >> >> The file creation is moved to the end of alloc_tag_init() as well. >> If alloc_tag_init() fails with alloc_tag_cttype still NULL or an >> error pointer, a concurrent reader of the leftover file would >> dereference it in allocinfo_start() and panic. >> >> Reported-by: Sashiko >> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression") >> Cc: stable@vger.kernel.org >> Signed-off-by: Hao Ge >> --- >> mm/alloc_tag.c | 26 +++++++++++++++++--------- >> 1 file changed, 17 insertions(+), 9 deletions(-) >> >> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c >> index 1ca0409b492b..cfa0fc84b68f 100644 >> --- a/mm/alloc_tag.c >> +++ b/mm/alloc_tag.c >> @@ -15,6 +15,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> >> @@ -591,6 +592,13 @@ void pgalloc_tag_swap(struct folio *new, struct folio *old) >> put_page_tag_ref(handle_new); >> } >> >> +static void remove_allocinfo_file(struct work_struct *work) >> +{ >> + remove_proc_entry(ALLOCINFO_FILE_NAME, NULL); >> +} >> + >> +static DECLARE_WORK(remove_allocinfo_work, remove_allocinfo_file); >> + >> static void shutdown_mem_profiling(bool remove_file) >> { >> if (mem_alloc_profiling_enabled()) >> @@ -600,7 +608,7 @@ static void shutdown_mem_profiling(bool remove_file) >> return; >> >> if (remove_file) >> - remove_proc_entry(ALLOCINFO_FILE_NAME, NULL); >> + schedule_work(&remove_allocinfo_work); >> mem_profiling_support = false; >> } >> >> @@ -1358,16 +1366,10 @@ static int __init alloc_tag_init(void) >> return 0; >> } >> >> - if (!proc_create(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_proc_ops)) { >> - pr_err("Failed to create %s file\n", ALLOCINFO_FILE_NAME); >> - shutdown_mem_profiling(false); >> - return -ENOMEM; >> - } >> - >> res = alloc_mod_tags_mem(); >> if (res) { >> pr_err("Failed to reserve address space for module tags, errno = %d\n", res); >> - shutdown_mem_profiling(true); >> + shutdown_mem_profiling(false); >> return res; >> } >> >> @@ -1375,10 +1377,16 @@ static int __init alloc_tag_init(void) >> if (IS_ERR(alloc_tag_cttype)) { >> pr_err("Allocation tags registration failed, errno = %pe\n", alloc_tag_cttype); >> free_mod_tags_mem(); >> - shutdown_mem_profiling(true); >> + shutdown_mem_profiling(false); >> return PTR_ERR(alloc_tag_cttype); >> } >> >> + if (!proc_create(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_proc_ops)) { >> + pr_err("Failed to create %s file\n", ALLOCINFO_FILE_NAME); >> + shutdown_mem_profiling(false); > > You need free_mod_tags_mem() here. > Right. Another problem is exposed here: moving proc_create() to the end implies successful return from codetag_register_type(), so alloc_tag is already added into codetag_types. That looks a bit odd to me. Because all places inside codetag that access this linked list will access this incompletely‑initialized codetag_type. There is currently no matching unregister interface to tear it down. So I drafted one previously: void codetag_unregister_type(struct codetag_type *cttype) { struct codetag_module *cmod; unsigned long id, tmp; mutex_lock(&codetag_lock); list_del(&cttype->link); mutex_unlock(&codetag_lock); codetag_lock_module_list(cttype); idr_for_each_entry_ul(&cttype->mod_idr, cmod, tmp, id) kfree(cmod); idr_destroy(&cttype->mod_idr); codetag_unlock_module_list(cttype); kfree(cttype); } But looking back, do we really need to do this? I'm not so sure. I previously thought the issue reported by Sashiko was a false positive, and I laid out my thoughts back then: https://lore.kernel.org/all/afa606df-3d5b-47c2-9972-f3e0c2e13c12@linux.dev/ and I thought the change would be straightforward, and defensive programming felt acceptable to me, but it turns out to be a little more complex than I expected. Suren, could you help me analyze this? Thank you very much for your valuable feedback Thanks Best Regards Hao >> + return -ENOMEM; >> + } >> + >> return 0; >> } >> module_init(alloc_tag_init); >> -- >> 2.25.1 >>