From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2B1863093DD; Fri, 12 Jun 2026 07:36:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781249765; cv=none; b=K0Z5ym7H7vVjmksO9w36xg6jGrDFHY2z5kdG5tdeaigyxA3+47kV7RjMn8jGmMA/qWOkmvHtJjK2BcZmdLlFxWlFhzWDkb5H7v9ATaEwLDYIdXDB3RpHmlK47O8WjzOp999/lImMir32y9YOwuHdmgHzBk0tuaZnNpIeM4g+JZ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781249765; c=relaxed/simple; bh=amWtrN9ebYHEFBhQNOxoiQaXTaktTxRaZK6iSH1pCGE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=P/8D9tjGrpVViJ3127eE2YBjuVDxUMvhTvfdTut+mRLO/HKZKsU7CfXllKAQ/f0P3HWjbvlSOEFx/92ci7YZlgs1qSpSvymR1H2trej1/rDLEeb1by31p2PvgzTFHRmEXIQIXwNZUkyHLHdrvW39W9hli/g3/oE80uNs6dq05Wc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YpHb8phY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YpHb8phY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB1AF1F000E9; Fri, 12 Jun 2026 07:36:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781249763; bh=kOX08Qpl3nLj8+/bGT7gMI+71ks0J39RDfqBI01e/bs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=YpHb8phYvCXL//PMNv6jJibMmIvbuZmFBd81SZPjBSMR8ToRShtN3aXcZQR5xRGOF 5D1aoLZGabiAlDqIpuffzOCx97pcxQ9zSS0/JgxMXO0J1HfPqTEC0I21xlyTI22bSc rD+sjQ6+hPGHfZzV1cRQjhR1zP4JNTPuaZ+xJ/FAeHV1xlSYiVsoxlMVjMqbpvaDCn qXB2IXqiuMyKCLM/AHpVj7C5sVFvpbcSlfU8SBPVkLFWPROv5ffLzAAo4FsdEkp6Vv GDjbVyismAzQ8Yj41kuEmLVoZ66puCR7NZaY5e7pk5iSCZXrGdKNdkltMZnHJIkraK nd5WalUl+cWLw== Message-ID: <09ee2ea0-c93f-406c-b5af-1fe3a50c8989@kernel.org> Date: Fri, 12 Jun 2026 09:36:00 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup_test: fix race with PIN_LONGTERM_TEST ioctls To: Yunhui Cui , akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, yang.lee@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org References: <20260608025043.88087-1-cuiyunhui@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/8/26 04:50, Yunhui Cui wrote: > The PIN_LONGTERM_TEST helpers keep their state in global variables that > are protected by pin_longterm_test_mutex when accessed from ioctl(). > However, gup_test_release() calls pin_longterm_test_stop() without > holding that mutex. > > This can race with PIN_LONGTERM_TEST_STOP and let two callers operate on > the same pages array concurrently, corrupting the test state and possibly > freeing it twice: > > CPU 0 CPU 1 > ----- ----- > ioctl(PIN_LONGTERM_TEST_STOP) > mutex_lock(&pin_longterm_test_mutex) > pin_longterm_test_stop() > if (pin_longterm_test_pages) > kvfree(pin_longterm_test_pages) > > close() > gup_test_release() > pin_longterm_test_stop() > if (pin_longterm_test_pages) > kvfree(pin_longterm_test_pages) > > pin_longterm_test_pages = NULL > mutex_unlock(&pin_longterm_test_mutex) Okay, thinking about this some more ... I think what's really required here is that we have two separate "struct file", because otherwise release() cannot race with unlocked_ioctl(). Which is something we didn't expect when we added this functionality. I think the proper way to handle this is by moving the state to the "struct file", to actually cleanly allow concurrent usage. So instead, I think we should do the following (untested): >From 29e3d6fe00c4bd843d11bb548efa89bca478436c Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Fri, 12 Jun 2026 09:22:25 +0200 Subject: [PATCH] mm/gup_test: keep longterm pin state per file The pin longterm test currently stores its data globally, shared among multiple concurrent users of the interface (multiple open file descriptors -> multiple "struct file"'s). That makes the gup_test interface problematic to use concurrently: two users, such as concurrent selftest runs, can interfere with the same longterm pin state. While this has not been observed as a problem so far in practice, let's just handle it cleanly. There could be a way to trigger selftest failures by e.g., running the cow.c and gup_longerm.c selftests concurrently, but we usually run them sequentially. Let's add a "Fixes" tag to be safe. Fixes: c77369b437f9 ("mm/gup_test: start/stop/read functionality for PIN LONGTERM test") Signed-off-by: David Hildenbrand (Arm) --- mm/gup_test.c | 93 +++++++++++++++++++++++++++++++++------------------ 1 file changed, 61 insertions(+), 32 deletions(-) diff --git a/mm/gup_test.c b/mm/gup_test.c index 9dd48db897b9..16916056677e 100644 --- a/mm/gup_test.c +++ b/mm/gup_test.c @@ -8,6 +8,12 @@ #include #include "gup_test.h" +struct gup_test_data { + struct mutex longterm_mutex; + struct page **longterm_pages; + unsigned long longterm_nr_pages; +}; + static void put_back_pages(unsigned int cmd, struct page **pages, unsigned long nr_pages, unsigned int gup_test_flags) { @@ -204,23 +210,20 @@ static int __gup_test_ioctl(unsigned int cmd, return ret; } -static DEFINE_MUTEX(pin_longterm_test_mutex); -static struct page **pin_longterm_test_pages; -static unsigned long pin_longterm_test_nr_pages; - -static inline void pin_longterm_test_stop(void) +static inline void pin_longterm_test_stop(struct gup_test_data *data) { - if (pin_longterm_test_pages) { - if (pin_longterm_test_nr_pages) - unpin_user_pages(pin_longterm_test_pages, - pin_longterm_test_nr_pages); - kvfree(pin_longterm_test_pages); - pin_longterm_test_pages = NULL; - pin_longterm_test_nr_pages = 0; + if (data->longterm_pages) { + if (data->longterm_nr_pages) + unpin_user_pages(data->longterm_pages, + data->longterm_nr_pages); + kvfree(data->longterm_pages); + data->longterm_pages = NULL; + data->longterm_nr_pages = 0; } } -static inline int pin_longterm_test_start(unsigned long arg) +static inline int pin_longterm_test_start(struct gup_test_data *data, + unsigned long arg) { long nr_pages, cur_pages, addr, remaining_pages; int gup_flags = FOLL_LONGTERM; @@ -229,7 +232,7 @@ static inline int pin_longterm_test_start(unsigned long arg) int ret = 0; bool fast; - if (pin_longterm_test_pages) + if (data->longterm_pages) return -EINVAL; if (copy_from_user(&args, (void __user *)arg, sizeof(args))) @@ -259,12 +262,12 @@ static inline int pin_longterm_test_start(unsigned long arg) return -EINTR; } - pin_longterm_test_pages = pages; - pin_longterm_test_nr_pages = 0; + data->longterm_pages = pages; + data->longterm_nr_pages = 0; - while (nr_pages - pin_longterm_test_nr_pages) { - remaining_pages = nr_pages - pin_longterm_test_nr_pages; - addr = args.addr + pin_longterm_test_nr_pages * PAGE_SIZE; + while (nr_pages - data->longterm_nr_pages) { + remaining_pages = nr_pages - data->longterm_nr_pages; + addr = args.addr + data->longterm_nr_pages * PAGE_SIZE; if (fast) cur_pages = pin_user_pages_fast(addr, remaining_pages, @@ -273,11 +276,11 @@ static inline int pin_longterm_test_start(unsigned long arg) cur_pages = pin_user_pages(addr, remaining_pages, gup_flags, pages); if (cur_pages < 0) { - pin_longterm_test_stop(); + pin_longterm_test_stop(data); ret = cur_pages; break; } - pin_longterm_test_nr_pages += cur_pages; + data->longterm_nr_pages += cur_pages; pages += cur_pages; } @@ -286,19 +289,20 @@ static inline int pin_longterm_test_start(unsigned long arg) return ret; } -static inline int pin_longterm_test_read(unsigned long arg) +static inline int pin_longterm_test_read(struct gup_test_data *data, + unsigned long arg) { __u64 user_addr; unsigned long i; - if (!pin_longterm_test_pages) + if (!data->longterm_pages) return -EINVAL; if (copy_from_user(&user_addr, (void __user *)arg, sizeof(user_addr))) return -EFAULT; - for (i = 0; i < pin_longterm_test_nr_pages; i++) { - void *addr = kmap_local_page(pin_longterm_test_pages[i]); + for (i = 0; i < data->longterm_nr_pages; i++) { + void *addr = kmap_local_page(data->longterm_pages[i]); unsigned long ret; ret = copy_to_user((void __user *)(unsigned long)user_addr, addr, @@ -314,25 +318,26 @@ static inline int pin_longterm_test_read(unsigned long arg) static long pin_longterm_test_ioctl(struct file *filep, unsigned int cmd, unsigned long arg) { + struct gup_test_data *data = filep->private_data; int ret = -EINVAL; - if (mutex_lock_killable(&pin_longterm_test_mutex)) + if (mutex_lock_killable(&data->longterm_mutex)) return -EINTR; switch (cmd) { case PIN_LONGTERM_TEST_START: - ret = pin_longterm_test_start(arg); + ret = pin_longterm_test_start(data, arg); break; case PIN_LONGTERM_TEST_STOP: - pin_longterm_test_stop(); + pin_longterm_test_stop(data); ret = 0; break; case PIN_LONGTERM_TEST_READ: - ret = pin_longterm_test_read(arg); + ret = pin_longterm_test_read(data, arg); break; } - mutex_unlock(&pin_longterm_test_mutex); + mutex_unlock(&data->longterm_mutex); return ret; } @@ -371,15 +376,39 @@ static long gup_test_ioctl(struct file *filep, unsigned int cmd, return 0; } +static int gup_test_open(struct inode *inode, struct file *file) +{ + struct gup_test_data *data; + int ret; + + data = kzalloc(sizeof(*data), GFP_KERNEL); + if (!data) + return -ENOMEM; + + ret = nonseekable_open(inode, file); + if (ret) { + kfree(data); + return ret; + } + + mutex_init(&data->longterm_mutex); + file->private_data = data; + return 0; +} + static int gup_test_release(struct inode *inode, struct file *file) { - pin_longterm_test_stop(); + struct gup_test_data *data = file->private_data; + + pin_longterm_test_stop(data); + kfree(data); + file->private_data = NULL; return 0; } static const struct file_operations gup_test_fops = { - .open = nonseekable_open, + .open = gup_test_open, .unlocked_ioctl = gup_test_ioctl, .compat_ioctl = compat_ptr_ioctl, .release = gup_test_release, -- 2.43.0 Can you review+test that change? Thanks! -- Cheers, David