From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8581A346FB5 for ; Tue, 9 Jun 2026 01:44:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780969451; cv=none; b=K4RYwOTYYCm5QI5wKmghiaXVCyUh2/xRMYCzMLC5PHgoeteTl2LxTfwbgSrGo0A9k9PCNcPwfWqdCRCkVWjKwAQ327N8vyx4fQyexdq0hTduonEu5K/QBOaEJNyfXzkdXQCmdQBruGRSVZLUpDD6Micr38lHl2V40R8GFFVny3k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780969451; c=relaxed/simple; bh=qAkKQ/LAkEszyHfX1YdCpuZNl6IoW85FCezUFWx55Ik=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tpnWpMNjAF7ObQTxUKAWqZFk9vYbDo0U4vDFTapdQ2TDliAAZ6yt8aRyb564bMVLY2crOCnXtm9jlbGngdqnJw4EenqHwQbRle+yLCOmG5PdkiY2dLDBzz3042RPaDaY4THx9je2Ul4uOiXLtJ1jaHK58CsPwQfLHZV70SXJi3M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=k6Q9WdvM; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="k6Q9WdvM" Message-ID: <2b7fa423-c721-4157-96ba-93bee5010044@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780969437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KN2NpTJpJ6jSCQrNwdqnWftbSZQXv3T7wLZL+abW+Ds=; b=k6Q9WdvM8HuZyQdPUOsfaVbJ1UgmF1LGHvXePtAJuA0I+QODdwbKHO3L0DEA6/YFqwMA4Z BTiDK7/2SvVFuaptwYYKRrx9iuWiWQnwWQfVhy5WqS1E1/MVWO9xKcWK7rq4uWQD3PIffS HyxDrPjyVpAezLlUh2OdXu6csZeciNw= Date: Tue, 9 Jun 2026 09:43:16 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 1/6] alloc_tag: add ioctl to /proc/allocinfo To: Abhishek Bapat Cc: Suren Baghdasaryan , Andrew Morton , Kent Overstreet , Shuah Khan , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sourav Panda References: <0e91fdd3a88dbe5220d15c4c8ff7b8f66e86af7c.1780701922.git.abhishekbapat@google.com> <41a7ebb9-1113-4f13-abbf-6f55d99d62f3@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Ge In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Abhishek On 2026/6/9 08:19, Abhishek Bapat wrote: > On Sun, Jun 7, 2026 at 6:53 PM Hao Ge wrote: >> Hi Suren and Abhishek >> >> >> Thanks for the new version. >> >> >> On 2026/6/6 07:36, Abhishek Bapat wrote: >>> From: Suren Baghdasaryan >>> >>> Add the following ioctl commands for /proc/allocinfo file: >>> >>> ALLOCINFO_IOC_CONTENT_ID - gets content identifier which can be used >>> to check whether the file content has changed specifically due to module >>> load/unload. Every time a module is loaded / unloaded, the returned >>> value will be different. By comparing the identifier value at the >>> beginning and at the end of the content retrieval operation, users can >>> validate retrieved information for consistency. >>> >>> ALLOCINFO_IOC_GET_AT - gets the record at the specified position. This >>> is the position of a record in /proc/allocinfo. >>> >>> ALLOCINFO_IOC_GET_NEXT - gets the record next to the last retrieved >>> one. If no records were previously retrieved, returns the first >>> record. >>> >>> Signed-off-by: Suren Baghdasaryan >>> Signed-off-by: Abhishek Bapat >>> --- >>> Documentation/mm/allocation-profiling.rst | 5 + >>> .../userspace-api/ioctl/ioctl-number.rst | 2 + >>> MAINTAINERS | 1 + >>> include/linux/codetag.h | 2 + >>> include/uapi/linux/alloc_tag.h | 54 ++++ >>> lib/alloc_tag.c | 232 +++++++++++++++++- >>> lib/codetag.c | 18 ++ >>> 7 files changed, 312 insertions(+), 2 deletions(-) >>> create mode 100644 include/uapi/linux/alloc_tag.h >>> >>> diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst >>> index 5389d241176a..c3a28467955f 100644 >>> --- a/Documentation/mm/allocation-profiling.rst >>> +++ b/Documentation/mm/allocation-profiling.rst >>> @@ -46,6 +46,11 @@ sysctl: >>> Runtime info: >>> /proc/allocinfo >>> >>> + Profiling data can be retrieved either by reading `/proc/allocinfo` directly as >>> + text or programmatically via `ioctl()` calls defined in ``. >>> + The ioctl interface supports structured binary data extraction as well as filtering >>> + by module name, function, file, line number, accuracy, or allocation size limits. >>> + >>> Example output:: >>> >>> root@moria-kvm:~# sort -g /proc/allocinfo|tail|numfmt --to=iec >>> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst >>> index 331223761fff..84f6808a8578 100644 >>> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst >>> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst >>> @@ -349,6 +349,8 @@ Code Seq# Include File Comments >>> >>> 0xA5 20-2F linux/surface_aggregator/dtx.h Microsoft Surface DTX driver >>> >>> +0xA6 00-0F uapi/linux/alloc_tag.h Memory allocation profiling >>> + >>> 0xAA 00-3F linux/uapi/linux/userfaultfd.h >>> 0xAB 00-1F linux/nbd.h >>> 0xAC 00-1F linux/raw.h >>> diff --git a/MAINTAINERS b/MAINTAINERS >>> index a31f6f207afd..77f3fc487691 100644 >>> --- a/MAINTAINERS >>> +++ b/MAINTAINERS >>> @@ -16711,6 +16711,7 @@ S: Maintained >>> F: Documentation/mm/allocation-profiling.rst >>> F: include/linux/alloc_tag.h >>> F: include/linux/pgalloc_tag.h >>> +F: include/uapi/linux/alloc_tag.h >>> F: lib/alloc_tag.c >>> >>> MEMORY CONTROLLER DRIVERS >>> diff --git a/include/linux/codetag.h b/include/linux/codetag.h >>> index ddae7484ca45..a25a085c2df1 100644 >>> --- a/include/linux/codetag.h >>> +++ b/include/linux/codetag.h >>> @@ -77,6 +77,8 @@ struct codetag_iterator { >>> void codetag_lock_module_list(struct codetag_type *cttype); >>> bool codetag_trylock_module_list(struct codetag_type *cttype); >>> void codetag_unlock_module_list(struct codetag_type *cttype); >>> +unsigned long codetag_get_content_id(struct codetag_type *cttype); >>> +unsigned int codetag_get_count(struct codetag_type *cttype); >>> struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype); >>> struct codetag *codetag_next_ct(struct codetag_iterator *iter); >>> >>> diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h >>> new file mode 100644 >>> index 000000000000..901199bad514 >>> --- /dev/null >>> +++ b/include/uapi/linux/alloc_tag.h >>> @@ -0,0 +1,54 @@ >>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ >>> +/* >>> + * include/linux/alloc_tag.h >> nit: it should be include/uapi/linux/alloc_tag.h >> >> (I guess you may have missed the comment I brought up before. It is not >> a critical problem though.) >> > Apologies, I missed that comment earlier. Included in the v4 patchset. > Thanks for bringing this up. > >>> + */ >>> + >>> +#ifndef _UAPI_ALLOC_TAG_H >>> +#define _UAPI_ALLOC_TAG_H >>> + >>> +#include >>> + >>> +#define ALLOCINFO_STR_SIZE 64 >>> + >>> +struct allocinfo_content_id { >>> + __u64 id; >>> +}; >>> + >>> +struct allocinfo_tag { >>> + /* Longer names are trimmed */ >>> + char modname[ALLOCINFO_STR_SIZE]; >>> + char function[ALLOCINFO_STR_SIZE]; >>> + char filename[ALLOCINFO_STR_SIZE]; >>> + __u64 lineno; >>> +}; >>> + >>> +/* The alignment ensures 32-bit compatible interfaces are not broken */ >>> +struct allocinfo_counter { >>> + __u64 bytes; >>> + __u64 calls; >>> + __u8 accurate; >>> +} __attribute__((aligned(8))); >>> + >>> +struct allocinfo_tag_data { >>> + struct allocinfo_tag tag; >>> + struct allocinfo_counter counter; >>> +}; >>> + >>> +struct allocinfo_get_at { >>> + __u64 pos; /* input */ >>> + struct allocinfo_tag_data data; >>> +}; >>> + >>> +#define _ALLOCINFO_IOC_CONTENT_ID 0 >>> +#define _ALLOCINFO_IOC_GET_AT 1 >>> +#define _ALLOCINFO_IOC_GET_NEXT 2 >>> + >>> +#define ALLOCINFO_IOC_BASE 0xA6 >>> +#define ALLOCINFO_IOC_CONTENT_ID _IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_CONTENT_ID, \ >>> + struct allocinfo_content_id) >>> +#define ALLOCINFO_IOC_GET_AT _IOWR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_AT, \ >>> + struct allocinfo_get_at) >>> +#define ALLOCINFO_IOC_GET_NEXT _IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_NEXT, \ >>> + struct allocinfo_tag_data) >>> + >>> +#endif /* _UAPI_ALLOC_TAG_H */ >>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c >>> index d9be1cf5187d..a0577215eb3d 100644 >>> --- a/lib/alloc_tag.c >>> +++ b/lib/alloc_tag.c >>> @@ -5,6 +5,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -14,6 +15,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> >>> #define ALLOCINFO_FILE_NAME "allocinfo" >>> #define MODULE_ALLOC_TAG_VMAP_SIZE (100000UL * sizeof(struct alloc_tag)) >>> @@ -47,6 +49,10 @@ struct allocinfo_private { >>> struct codetag_iterator iter; >>> struct codetag_iterator reported_iter; >>> bool print_header; >>> + /* ioctl uses a separate iterator not to interfere with reads */ >>> + struct codetag_iterator ioctl_iter; >>> + bool positioned; /* seq_open_private() sets to 0 */ >>> + struct mutex ioctl_lock; >>> }; >>> >>> static void *allocinfo_start(struct seq_file *m, loff_t *pos) >>> @@ -130,6 +136,229 @@ static const struct seq_operations allocinfo_seq_op = { >>> .show = allocinfo_show, >>> }; >>> >>> +/* >>> + * Initializes seq_file operations and allocates private state when opening >>> + * the /proc/allocinfo procfs entry. >>> + */ >>> +static int allocinfo_open(struct inode *inode, struct file *file) >>> +{ >>> + int ret; >>> + >>> + ret = seq_open_private(file, &allocinfo_seq_op, >>> + sizeof(struct allocinfo_private)); >>> + if (!ret) { >>> + struct seq_file *m = file->private_data; >>> + struct allocinfo_private *priv = m->private; >>> + >>> + mutex_init(&priv->ioctl_lock); >>> + } >>> + return ret; >>> +} >>> + >>> +/* >>> + * Cleans up the seq_file state and frees up the private state allocated in >>> + * allocinfo_open() when closing the /proc/allocinfo file descriptor. >>> + */ >>> +static int allocinfo_release(struct inode *inode, struct file *file) >>> +{ >>> + return seq_release_private(inode, file); >>> +} >>> + >>> +/* >>> + * Returns a pointer to the suffix of a string so that its length fits within >>> + * ALLOCINFO_STR_SIZE, preserving the trailing characters. >>> + */ >>> +static const char *allocinfo_str(const char *str) >>> +{ >>> + size_t len = strlen(str); >>> + >>> + /* Keep an extra space for the trailing NULL. */ >>> + if (len >= ALLOCINFO_STR_SIZE) >>> + str += (len - ALLOCINFO_STR_SIZE) + 1; >>> + return str; >>> +} >>> + >>> +/* Copy a string and trim from the beginning if it's too long */ >>> +static void allocinfo_copy_str(char *dest, const char *src) >>> +{ >>> + strscpy_pad(dest, allocinfo_str(src), ALLOCINFO_STR_SIZE); >>> +} >>> + >>> +/* >>> + * Populates the UAPI allocinfo_tag_data structure with active runtime >>> + * profiling counters extracted from the given kernel codetag. >>> + */ >>> +static void allocinfo_to_params(struct codetag *ct, >>> + struct allocinfo_tag_data *data) >>> +{ >>> + struct alloc_tag *tag = ct_to_alloc_tag(ct); >>> + struct alloc_tag_counters counter = alloc_tag_read(tag); >>> + >>> + if (ct->modname) >>> + allocinfo_copy_str(data->tag.modname, ct->modname); >>> + else >>> + data->tag.modname[0] = '\0'; >>> + allocinfo_copy_str(data->tag.function, ct->function); >>> + allocinfo_copy_str(data->tag.filename, ct->filename); >>> + data->tag.lineno = ct->lineno; >>> + data->counter.bytes = counter.bytes; >>> + data->counter.calls = counter.calls; >>> + data->counter.accurate = !alloc_tag_is_inaccurate(tag); >>> +} >>> + >>> +/* >>> + * Retrieves the unique content ID representing the current allocation tag module >>> + * layout, allowing userspace to detect if modules were loaded / unloaded. >>> + */ >>> +static int allocinfo_ioctl_get_content_id(struct seq_file *m, void __user *arg) >>> +{ >>> + struct allocinfo_content_id params; >>> + >>> + codetag_lock_module_list(alloc_tag_cttype); >>> + params.id = codetag_get_content_id(alloc_tag_cttype); >>> + codetag_unlock_module_list(alloc_tag_cttype); >>> + if (copy_to_user(arg, ¶ms, sizeof(params))) >>> + return -EFAULT; >>> + >>> + return 0; >>> +} >>> + >>> +/* >>> + * Seeks the ioctl iterator to the specified 0-indexed tag position, reads its >>> + * profiling data and returns it to userspace. >>> + */ >>> +static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg) >>> +{ >>> + struct allocinfo_private *priv; >>> + struct codetag *ct; >>> + __u64 pos; >>> + struct allocinfo_get_at params = {0}; >>> + >>> + if (copy_from_user(¶ms, arg, sizeof(params))) >>> + return -EFAULT; >>> + >>> + priv = m->private; >>> + pos = params.pos; >>> + >>> + mutex_lock(&priv->ioctl_lock); >>> + codetag_lock_module_list(alloc_tag_cttype); >>> + >>> + if (pos >= codetag_get_count(alloc_tag_cttype)) { >>> + codetag_unlock_module_list(alloc_tag_cttype); >>> + mutex_unlock(&priv->ioctl_lock); >>> + return -ENOENT; >>> + } >>> + >>> + /* Find the codetag */ >>> + priv->ioctl_iter = codetag_get_ct_iter(alloc_tag_cttype); >>> + ct = codetag_next_ct(&priv->ioctl_iter); >>> + while (ct && pos--) >>> + ct = codetag_next_ct(&priv->ioctl_iter); >>> + if (ct) { >>> + allocinfo_to_params(ct, ¶ms.data); >>> + priv->positioned = true; >>> + } >>> + >>> + codetag_unlock_module_list(alloc_tag_cttype); >>> + mutex_unlock(&priv->ioctl_lock); >>> + >>> + if (!ct) >>> + return -ENOENT; >>> + >>> + if (copy_to_user(arg, ¶ms, sizeof(params))) >>> + return -EFAULT; >>> + >>> + return 0; >>> +} >>> + >>> +/* >>> + * Advances the ioctl iterator to the next allocation tag in the sequence and >>> + * returns its profiling data to userspace. >>> + */ >>> +static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg) >>> +{ >>> + struct allocinfo_private *priv; >>> + struct codetag *ct; >>> + struct allocinfo_tag_data params; >>> + int ret = 0; >>> + >>> + memset(¶ms, 0, sizeof(params)); >>> + priv = m->private; >>> + >>> + mutex_lock(&priv->ioctl_lock); >>> + codetag_lock_module_list(alloc_tag_cttype); >>> + >>> + if (!priv->positioned) { >>> + priv->ioctl_iter = codetag_get_ct_iter(alloc_tag_cttype); >>> + priv->positioned = true; >>> + } >>> + >>> + ct = codetag_next_ct(&priv->ioctl_iter); >>> + if (ct) >>> + allocinfo_to_params(ct, ¶ms); >>> + >>> + if (!ct) { >>> + priv->positioned = false; >>> + ret = -ENOENT; >>> + } >>> + codetag_unlock_module_list(alloc_tag_cttype); >>> + mutex_unlock(&priv->ioctl_lock); >>> + >>> + if (ret == 0) { >>> + if (copy_to_user(arg, ¶ms, sizeof(params))) >>> + return -EFAULT; >>> + } >>> + return ret; >>> +} >>> + >>> +/* >>> + * Entry point ioctl function for /proc/allocinfo routing requests to fetch the >>> + * layout content ID, seek to a specific tag, or read sequential tags. >>> + */ >>> +static long allocinfo_ioctl(struct file *file, unsigned int cmd, >>> + unsigned long __arg) >>> +{ >>> + void __user *arg = (void __user *)__arg; >>> + int ret; >>> + >>> + switch (cmd) { >>> + case ALLOCINFO_IOC_CONTENT_ID: >>> + ret = allocinfo_ioctl_get_content_id(file->private_data, arg); >>> + break; >>> + case ALLOCINFO_IOC_GET_AT: >>> + ret = allocinfo_ioctl_get_at(file->private_data, arg); >>> + break; >>> + case ALLOCINFO_IOC_GET_NEXT: >>> + ret = allocinfo_ioctl_get_next(file->private_data, arg); >>> + break; >>> + default: >>> + ret = -ENOIOCTLCMD; >>> + break; >>> + } >>> + >>> + return ret; >>> +} >>> + >>> +#ifdef CONFIG_COMPAT >>> +static long allocinfo_compat_ioctl(struct file *file, unsigned int cmd, >>> + unsigned long arg) >>> +{ >>> + return allocinfo_ioctl(file, cmd, (unsigned long)compat_ptr(arg)); >>> +} >>> +#endif >>> + >>> +static const struct proc_ops allocinfo_proc_ops = { >>> + .proc_open = allocinfo_open, >>> + .proc_read_iter = seq_read_iter, >>> + .proc_lseek = seq_lseek, >>> + .proc_release = allocinfo_release, >>> + .proc_ioctl = allocinfo_ioctl, >>> +#ifdef CONFIG_COMPAT >>> + .proc_compat_ioctl = allocinfo_compat_ioctl, >>> +#endif >>> + >>> +}; >>> + >>> size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep) >>> { >>> struct codetag_iterator iter; >>> @@ -993,8 +1222,7 @@ static int __init alloc_tag_init(void) >>> return 0; >>> } >>> >>> - if (!proc_create_seq_private(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_seq_op, >>> - sizeof(struct allocinfo_private), NULL)) { >>> + 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; >>> diff --git a/lib/codetag.c b/lib/codetag.c >>> index 4001a7ea6675..a9cda4c962a3 100644 >>> --- a/lib/codetag.c >>> +++ b/lib/codetag.c >>> @@ -19,6 +19,8 @@ struct codetag_type { >>> struct codetag_type_desc desc; >>> /* generates unique sequence number for module load */ >>> unsigned long next_mod_seq; >>> + /* bumped on every module load and unload */ >>> + unsigned long content_id; >>> }; >>> >>> struct codetag_range { >>> @@ -50,6 +52,20 @@ void codetag_unlock_module_list(struct codetag_type *cttype) >>> up_read(&cttype->mod_lock); >>> } >>> >>> +unsigned long codetag_get_content_id(struct codetag_type *cttype) >>> +{ >>> + lockdep_assert_held(&cttype->mod_lock); >>> + >>> + return cttype->content_id; >>> +} >>> + >>> +unsigned int codetag_get_count(struct codetag_type *cttype) >>> +{ >>> + lockdep_assert_held(&cttype->mod_lock); >>> + >>> + return cttype->count; >>> +} >>> + >>> struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype) >>> { >>> struct codetag_iterator iter = { >>> @@ -204,6 +220,7 @@ static int codetag_module_init(struct codetag_type *cttype, struct module *mod) >>> >>> down_write(&cttype->mod_lock); >>> cmod->mod_seq = ++cttype->next_mod_seq; >>> + ++cttype->content_id; >> I have a comment on the content_id bump placement. >> >> ++cttype->content_id is placed before idr_alloc and the module_load >> >> callback. If idr_alloc fails or module_load returns an error >> >> (While the chance of this occurring is very low.), the idr entry gets >> >> rolled back but content_id has already been bumped. The actual >> >> content didn't change in this case, so userspace would see a >> >> different content_id and assume the data is inconsistent when it >> >> isn't. >> >> >> Thanks >> >> Best Regards >> >> Hao > While I agree with your comment, I decided to place the counter > increment there because the chance of failure is low. Furthermore, > even if it falsely invalidates user data, the user will simply query > the content again. This placement also aligns with where the > previously used field (cttype->next_mod_seq) was incremented. Let me > know if you still think I should move it. Thanks! Sorry, I should have marked this as a nit when I raised the comment. Given its low probability of occurring, it doesn't block anything for now. The reason I raised this comment was just in case someone adds new logic in the feature  that could fail. But if that happens, we can move both next_mod_seq and content_id down together. Thanks Best Regards Hao >>> mod_id = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL); >>> if (mod_id >= 0) { >>> if (cttype->desc.module_load) { >>> @@ -368,6 +385,7 @@ void codetag_unload_module(struct module *mod) >>> cttype->count -= range_size(cttype, &cmod->range); >>> idr_remove(&cttype->mod_idr, mod_id); >>> kfree(cmod); >>> + ++cttype->content_id; >>> } >>> up_write(&cttype->mod_lock); >>> if (found && cttype->desc.free_section_mem)