+ selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch added to mm-new branch

+ selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch added to mm-new branch

[Andrew Morton]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 7881 bytes --]


The patch titled
     Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
has been added to the -mm mm-new branch.  Its filename is
     selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
Date: Tue, 24 Jun 2025 12:33:55 -0700

Test that /proc/pid/maps does not report unexpected holes in the address
space when we concurrently remap a part of a vma into the middle of
another vma.  This remapping results in the destination vma being split
into three parts and the part in the middle being patched back from, all
done concurrently from under the reader.  We should always see either
original vma or the split one with no holes.

Link: https://lkml.kernel.org/r/20250624193359.3865351-4-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Ye Bin <yebin10@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/proc/proc-pid-vm.c |   92 +++++++++++++++++++
 1 file changed, 92 insertions(+)

--- a/tools/testing/selftests/proc/proc-pid-vm.c~selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping
+++ a/tools/testing/selftests/proc/proc-pid-vm.c
@@ -663,6 +663,95 @@ static void test_maps_tearing_from_resiz
 	signal_state(mod_info, TEST_DONE);
 }
 
+static inline void remap_vma(const struct vma_modifier_info *mod_info)
+{
+	/*
+	 * Remap the last page of the next vma into the middle of the vma.
+	 * This splits the current vma and the first and middle parts (the
+	 * parts at lower addresses) become the last vma objserved in the
+	 * first page and the first vma observed in the last page.
+	 */
+	assert(mremap(mod_info->next_addr + page_size * 2, page_size,
+		      page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+		      mod_info->addr + page_size) != MAP_FAILED);
+}
+
+static inline void patch_vma(const struct vma_modifier_info *mod_info)
+{
+	assert(!mprotect(mod_info->addr + page_size, page_size,
+			 mod_info->prot));
+}
+
+static inline void check_remap_result(struct line_content *mod_last_line,
+				      struct line_content *mod_first_line,
+				      struct line_content *restored_last_line,
+				      struct line_content *restored_first_line)
+{
+	/* Make sure vmas at the boundaries are changing */
+	assert(strcmp(mod_last_line->text, restored_last_line->text) != 0);
+	assert(strcmp(mod_first_line->text, restored_first_line->text) != 0);
+}
+
+static void test_maps_tearing_from_remap(int maps_fd,
+				struct vma_modifier_info *mod_info,
+				struct page_content *page1,
+				struct page_content *page2,
+				struct line_content *last_line,
+				struct line_content *first_line)
+{
+	struct line_content remapped_last_line;
+	struct line_content remapped_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
+
+	mod_info->vma_modify = remap_vma;
+	mod_info->vma_restore = patch_vma;
+	mod_info->vma_mod_check = check_remap_result;
+
+	capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
+			    &remapped_last_line, &remapped_first_line,
+			    &restored_last_line, &restored_first_line);
+
+	/* Now start concurrent modifications for test_duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	do {
+		read_boundary_lines(maps_fd, page1, page2, &new_last_line, &new_first_line);
+
+		/* Check if we read vmas after remapping it */
+		if (!strcmp(new_last_line.text, remapped_last_line.text)) {
+			/*
+			 * The vmas should be consistent with remap results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as split one, then
+			 * as restored one) because we found it as the next vma
+			 * again. In that case new first line will be the same
+			 * as the last restored line.
+			 */
+			assert(!strcmp(new_first_line.text, remapped_first_line.text) ||
+			       !strcmp(new_first_line.text, restored_last_line.text));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			assert(!strcmp(new_last_line.text, restored_last_line.text) &&
+			       !strcmp(new_first_line.text, restored_first_line.text));
+		}
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+	} while (end_ts.tv_sec - start_ts.tv_sec < test_duration_sec);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
 static int test_maps_tearing(void)
 {
 	struct vma_modifier_info *mod_info;
@@ -757,6 +846,9 @@ static int test_maps_tearing(void)
 	test_maps_tearing_from_resize(maps_fd, mod_info, &page1, &page2,
 				      &last_line, &first_line);
 
+	test_maps_tearing_from_remap(maps_fd, mod_info, &page1, &page2,
+				     &last_line, &first_line);
+
 	stop_vma_modifier(mod_info);
 
 	free(page2.data);
_

Patches currently in -mm which might be from surenb@google.com are

selftests-proc-add-proc-pid-maps-tearing-from-vma-split-test.patch
selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-resizing.patch
selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
selftests-proc-test-procmap_query-ioctl-while-vma-is-concurrently-modified.patch
selftests-proc-add-verbose-more-for-tests-to-facilitate-debugging.patch
mm-maps-read-proc-pid-maps-under-per-vma-lock.patch
mm-maps-execute-procmap_query-ioctl-under-per-vma-locks.patch

Re: + selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch added to mm-new branch

[Alexey Dobriyan]

On Tue, Jun 24, 2025 at 01:08:01PM -0700, Andrew Morton wrote:
> 
> The patch titled
>      Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
> has been added to the -mm mm-new branch.  Its filename is
>      selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
> 
> This patch will shortly appear at
>      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
> 
> This patch will later appear in the mm-new branch at
>     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> Note, mm-new is a provisional staging ground for work-in-progress
> patches, and acceptance into mm-new is a notification for others take
> notice and to finish up reviews.  Please do not hesitate to respond to
> review feedback and post updated versions to replace or incrementally
> fixup patches in mm-new.
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
> 
> ------------------------------------------------------
> From: Suren Baghdasaryan <surenb@google.com>
> Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
> Date: Tue, 24 Jun 2025 12:33:55 -0700
> 
> Test that /proc/pid/maps does not report unexpected holes in the address
> space when we concurrently remap a part of a vma into the middle of
> another vma.  This remapping results in the destination vma being split
> into three parts and the part in the middle being patched back from, all
> done concurrently from under the reader.  We should always see either
> original vma or the split one with no holes.
> 
> Link: https://lkml.kernel.org/r/20250624193359.3865351-4-surenb@google.com
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Jann Horn <jannh@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: Kalesh Singh <kaleshsingh@google.com>
> Cc: Liam Howlett <liam.howlett@oracle.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: "Paul E . McKenney" <paulmck@kernel.org>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Thomas Weißschuh <linux@weissschuh.net>
> Cc: T.J. Mercier <tjmercier@google.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Ye Bin <yebin10@huawei.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  tools/testing/selftests/proc/proc-pid-vm.c |   92 +++++++++++++++++++
>  1 file changed, 92 insertions(+)
> 
> --- a/tools/testing/selftests/proc/proc-pid-vm.c~selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping
> +++ a/tools/testing/selftests/proc/proc-pid-vm.c
> @@ -663,6 +663,95 @@ static void test_maps_tearing_from_resiz
>  	signal_state(mod_info, TEST_DONE);
>  }
>  
> +static inline void remap_vma(const struct vma_modifier_info *mod_info)
> +{
> +	/*
> +	 * Remap the last page of the next vma into the middle of the vma.
> +	 * This splits the current vma and the first and middle parts (the
> +	 * parts at lower addresses) become the last vma objserved in the
> +	 * first page and the first vma observed in the last page.
> +	 */
> +	assert(mremap(mod_info->next_addr + page_size * 2, page_size,
> +		      page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
> +		      mod_info->addr + page_size) != MAP_FAILED);
> +}
> +
> +static inline void patch_vma(const struct vma_modifier_info *mod_info)
> +{
> +	assert(!mprotect(mod_info->addr + page_size, page_size,
> +			 mod_info->prot));
> +}
> +
> +static inline void check_remap_result(struct line_content *mod_last_line,
> +				      struct line_content *mod_first_line,
> +				      struct line_content *restored_last_line,
> +				      struct line_content *restored_first_line)
> +{
> +	/* Make sure vmas at the boundaries are changing */
> +	assert(strcmp(mod_last_line->text, restored_last_line->text) != 0);
> +	assert(strcmp(mod_first_line->text, restored_first_line->text) != 0);
> +}
> +
> +static void test_maps_tearing_from_remap(int maps_fd,
> +				struct vma_modifier_info *mod_info,
> +				struct page_content *page1,
> +				struct page_content *page2,
> +				struct line_content *last_line,
> +				struct line_content *first_line)
> +{
> +	struct line_content remapped_last_line;
> +	struct line_content remapped_first_line;
> +	struct line_content restored_last_line;
> +	struct line_content restored_first_line;
> +
> +	wait_for_state(mod_info, SETUP_READY);
> +
> +	/* re-read the file to avoid using stale data from previous test */
> +	read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
> +
> +	mod_info->vma_modify = remap_vma;
> +	mod_info->vma_restore = patch_vma;
> +	mod_info->vma_mod_check = check_remap_result;
> +
> +	capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
> +			    &remapped_last_line, &remapped_first_line,
> +			    &restored_last_line, &restored_first_line);
> +
> +	/* Now start concurrent modifications for test_duration_sec */
> +	signal_state(mod_info, TEST_READY);
> +
> +	struct line_content new_last_line;
> +	struct line_content new_first_line;
> +	struct timespec start_ts, end_ts;
> +
> +	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
> +	do {
> +		read_boundary_lines(maps_fd, page1, page2, &new_last_line, &new_first_line);
> +
> +		/* Check if we read vmas after remapping it */
> +		if (!strcmp(new_last_line.text, remapped_last_line.text)) {
> +			/*
> +			 * The vmas should be consistent with remap results,
> +			 * however if the vma was concurrently restored, it
> +			 * can be reported twice (first as split one, then
> +			 * as restored one) because we found it as the next vma
> +			 * again. In that case new first line will be the same
> +			 * as the last restored line.
> +			 */
> +			assert(!strcmp(new_first_line.text, remapped_first_line.text) ||
> +			       !strcmp(new_first_line.text, restored_last_line.text));
> +		} else {
> +			/* The vmas should be consistent with the original/resored state */
> +			assert(!strcmp(new_last_line.text, restored_last_line.text) &&
> +			       !strcmp(new_first_line.text, restored_first_line.text));

Pro-tip: long asserts with || can be written as

	if (cond1) {
	} else if (cond2) {
	} else {
		assert(false);
	}

and long asserts with && should be written as

	assert(cond1);
	assert(cond2);

so that you know which one is broken when it happens.

But maybe not, if you're printing buggy contents anyway.

Re: + selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch added to mm-new branch

[Suren Baghdasaryan]

On Sat, Jun 28, 2025 at 7:25 AM Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
> On Tue, Jun 24, 2025 at 01:08:01PM -0700, Andrew Morton wrote:
> >
> > The patch titled
> >      Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
> > has been added to the -mm mm-new branch.  Its filename is
> >      selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
> >
> > This patch will shortly appear at
> >      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
> >
> > This patch will later appear in the mm-new branch at
> >     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> >
> > Note, mm-new is a provisional staging ground for work-in-progress
> > patches, and acceptance into mm-new is a notification for others take
> > notice and to finish up reviews.  Please do not hesitate to respond to
> > review feedback and post updated versions to replace or incrementally
> > fixup patches in mm-new.
> >
> > Before you just go and hit "reply", please:
> >    a) Consider who else should be cc'ed
> >    b) Prefer to cc a suitable mailing list as well
> >    c) Ideally: find the original patch on the mailing list and do a
> >       reply-to-all to that, adding suitable additional cc's
> >
> > *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> >
> > The -mm tree is included into linux-next via the mm-everything
> > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> > and is updated there every 2-3 working days
> >
> > ------------------------------------------------------
> > From: Suren Baghdasaryan <surenb@google.com>
> > Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
> > Date: Tue, 24 Jun 2025 12:33:55 -0700
> >
> > Test that /proc/pid/maps does not report unexpected holes in the address
> > space when we concurrently remap a part of a vma into the middle of
> > another vma.  This remapping results in the destination vma being split
> > into three parts and the part in the middle being patched back from, all
> > done concurrently from under the reader.  We should always see either
> > original vma or the split one with no holes.
> >
> > Link: https://lkml.kernel.org/r/20250624193359.3865351-4-surenb@google.com
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > Cc: Alexey Dobriyan <adobriyan@gmail.com>
> > Cc: Andrii Nakryiko <andrii@kernel.org>
> > Cc: Christian Brauner <brauner@kernel.org>
> > Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: Jann Horn <jannh@google.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: Josef Bacik <josef@toxicpanda.com>
> > Cc: Kalesh Singh <kaleshsingh@google.com>
> > Cc: Liam Howlett <liam.howlett@oracle.com>
> > Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Cc: Oscar Salvador <osalvador@suse.de>
> > Cc: "Paul E . McKenney" <paulmck@kernel.org>
> > Cc: Peter Xu <peterx@redhat.com>
> > Cc: Ryan Roberts <ryan.roberts@arm.com>
> > Cc: Shuah Khan <shuah@kernel.org>
> > Cc: Thomas Weißschuh <linux@weissschuh.net>
> > Cc: T.J. Mercier <tjmercier@google.com>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Ye Bin <yebin10@huawei.com>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >
> >  tools/testing/selftests/proc/proc-pid-vm.c |   92 +++++++++++++++++++
> >  1 file changed, 92 insertions(+)
> >
> > --- a/tools/testing/selftests/proc/proc-pid-vm.c~selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping
> > +++ a/tools/testing/selftests/proc/proc-pid-vm.c
> > @@ -663,6 +663,95 @@ static void test_maps_tearing_from_resiz
> >       signal_state(mod_info, TEST_DONE);
> >  }
> >
> > +static inline void remap_vma(const struct vma_modifier_info *mod_info)
> > +{
> > +     /*
> > +      * Remap the last page of the next vma into the middle of the vma.
> > +      * This splits the current vma and the first and middle parts (the
> > +      * parts at lower addresses) become the last vma objserved in the
> > +      * first page and the first vma observed in the last page.
> > +      */
> > +     assert(mremap(mod_info->next_addr + page_size * 2, page_size,
> > +                   page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
> > +                   mod_info->addr + page_size) != MAP_FAILED);
> > +}
> > +
> > +static inline void patch_vma(const struct vma_modifier_info *mod_info)
> > +{
> > +     assert(!mprotect(mod_info->addr + page_size, page_size,
> > +                      mod_info->prot));
> > +}
> > +
> > +static inline void check_remap_result(struct line_content *mod_last_line,
> > +                                   struct line_content *mod_first_line,
> > +                                   struct line_content *restored_last_line,
> > +                                   struct line_content *restored_first_line)
> > +{
> > +     /* Make sure vmas at the boundaries are changing */
> > +     assert(strcmp(mod_last_line->text, restored_last_line->text) != 0);
> > +     assert(strcmp(mod_first_line->text, restored_first_line->text) != 0);
> > +}
> > +
> > +static void test_maps_tearing_from_remap(int maps_fd,
> > +                             struct vma_modifier_info *mod_info,
> > +                             struct page_content *page1,
> > +                             struct page_content *page2,
> > +                             struct line_content *last_line,
> > +                             struct line_content *first_line)
> > +{
> > +     struct line_content remapped_last_line;
> > +     struct line_content remapped_first_line;
> > +     struct line_content restored_last_line;
> > +     struct line_content restored_first_line;
> > +
> > +     wait_for_state(mod_info, SETUP_READY);
> > +
> > +     /* re-read the file to avoid using stale data from previous test */
> > +     read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
> > +
> > +     mod_info->vma_modify = remap_vma;
> > +     mod_info->vma_restore = patch_vma;
> > +     mod_info->vma_mod_check = check_remap_result;
> > +
> > +     capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
> > +                         &remapped_last_line, &remapped_first_line,
> > +                         &restored_last_line, &restored_first_line);
> > +
> > +     /* Now start concurrent modifications for test_duration_sec */
> > +     signal_state(mod_info, TEST_READY);
> > +
> > +     struct line_content new_last_line;
> > +     struct line_content new_first_line;
> > +     struct timespec start_ts, end_ts;
> > +
> > +     clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
> > +     do {
> > +             read_boundary_lines(maps_fd, page1, page2, &new_last_line, &new_first_line);
> > +
> > +             /* Check if we read vmas after remapping it */
> > +             if (!strcmp(new_last_line.text, remapped_last_line.text)) {
> > +                     /*
> > +                      * The vmas should be consistent with remap results,
> > +                      * however if the vma was concurrently restored, it
> > +                      * can be reported twice (first as split one, then
> > +                      * as restored one) because we found it as the next vma
> > +                      * again. In that case new first line will be the same
> > +                      * as the last restored line.
> > +                      */
> > +                     assert(!strcmp(new_first_line.text, remapped_first_line.text) ||
> > +                            !strcmp(new_first_line.text, restored_last_line.text));
> > +             } else {
> > +                     /* The vmas should be consistent with the original/resored state */
> > +                     assert(!strcmp(new_last_line.text, restored_last_line.text) &&
> > +                            !strcmp(new_first_line.text, restored_first_line.text));
>
> Pro-tip: long asserts with || can be written as
>
>         if (cond1) {
>         } else if (cond2) {
>         } else {
>                 assert(false);
>         }
>
> and long asserts with && should be written as
>
>         assert(cond1);
>         assert(cond2);
>
> so that you know which one is broken when it happens.

Thanks! I'll revise considering your input.

>
> But maybe not, if you're printing buggy contents anyway.

+ selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch added to mm-new branch

[Andrew Morton]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 8024 bytes --]


The patch titled
     Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
has been added to the -mm mm-new branch.  Its filename is
     selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
Date: Thu, 3 Jul 2025 23:07:21 -0700

Test that /proc/pid/maps does not report unexpected holes in the address
space when we concurrently remap a part of a vma into the middle of
another vma.  This remapping results in the destination vma being split
into three parts and the part in the middle being patched back from, all
done concurrently from under the reader.  We should always see either
original vma or the split one with no holes.

Link: https://lkml.kernel.org/r/20250704060727.724817-4-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jeongjun Park <aha310510@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Ye Bin <yebin10@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/proc/proc-maps-race.c |   92 ++++++++++++++++
 1 file changed, 92 insertions(+)

--- a/tools/testing/selftests/proc/proc-maps-race.c~selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping
+++ a/tools/testing/selftests/proc/proc-maps-race.c
@@ -416,6 +416,95 @@ static void test_maps_tearing_from_resiz
 	signal_state(mod_info, TEST_DONE);
 }
 
+static inline void remap_vma(const struct vma_modifier_info *mod_info)
+{
+	/*
+	 * Remap the last page of the next vma into the middle of the vma.
+	 * This splits the current vma and the first and middle parts (the
+	 * parts at lower addresses) become the last vma objserved in the
+	 * first page and the first vma observed in the last page.
+	 */
+	assert(mremap(mod_info->next_addr + page_size * 2, page_size,
+		      page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+		      mod_info->addr + page_size) != MAP_FAILED);
+}
+
+static inline void patch_vma(const struct vma_modifier_info *mod_info)
+{
+	assert(!mprotect(mod_info->addr + page_size, page_size,
+			 mod_info->prot));
+}
+
+static inline void check_remap_result(struct line_content *mod_last_line,
+				      struct line_content *mod_first_line,
+				      struct line_content *restored_last_line,
+				      struct line_content *restored_first_line)
+{
+	/* Make sure vmas at the boundaries are changing */
+	assert(strcmp(mod_last_line->text, restored_last_line->text) != 0);
+	assert(strcmp(mod_first_line->text, restored_first_line->text) != 0);
+}
+
+static void test_maps_tearing_from_remap(int maps_fd,
+				struct vma_modifier_info *mod_info,
+				struct page_content *page1,
+				struct page_content *page2,
+				struct line_content *last_line,
+				struct line_content *first_line)
+{
+	struct line_content remapped_last_line;
+	struct line_content remapped_first_line;
+	struct line_content restored_last_line;
+	struct line_content restored_first_line;
+
+	wait_for_state(mod_info, SETUP_READY);
+
+	/* re-read the file to avoid using stale data from previous test */
+	read_boundary_lines(maps_fd, page1, page2, last_line, first_line);
+
+	mod_info->vma_modify = remap_vma;
+	mod_info->vma_restore = patch_vma;
+	mod_info->vma_mod_check = check_remap_result;
+
+	capture_mod_pattern(maps_fd, mod_info, page1, page2, last_line, first_line,
+			    &remapped_last_line, &remapped_first_line,
+			    &restored_last_line, &restored_first_line);
+
+	/* Now start concurrent modifications for test_duration_sec */
+	signal_state(mod_info, TEST_READY);
+
+	struct line_content new_last_line;
+	struct line_content new_first_line;
+	struct timespec start_ts, end_ts;
+
+	clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts);
+	do {
+		read_boundary_lines(maps_fd, page1, page2, &new_last_line, &new_first_line);
+
+		/* Check if we read vmas after remapping it */
+		if (!strcmp(new_last_line.text, remapped_last_line.text)) {
+			/*
+			 * The vmas should be consistent with remap results,
+			 * however if the vma was concurrently restored, it
+			 * can be reported twice (first as split one, then
+			 * as restored one) because we found it as the next vma
+			 * again. In that case new first line will be the same
+			 * as the last restored line.
+			 */
+			assert(!strcmp(new_first_line.text, remapped_first_line.text) ||
+			       !strcmp(new_first_line.text, restored_last_line.text));
+		} else {
+			/* The vmas should be consistent with the original/resored state */
+			assert(!strcmp(new_last_line.text, restored_last_line.text) &&
+			       !strcmp(new_first_line.text, restored_first_line.text));
+		}
+		clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts);
+	} while (end_ts.tv_sec - start_ts.tv_sec < test_duration_sec);
+
+	/* Signal the modifyer thread to stop and wait until it exits */
+	signal_state(mod_info, TEST_DONE);
+}
+
 int usage(void)
 {
 	fprintf(stderr, "Userland /proc/pid/{s}maps race test cases\n");
@@ -527,6 +616,9 @@ int main(int argc, char **argv)
 	test_maps_tearing_from_resize(maps_fd, mod_info, &page1, &page2,
 				      &last_line, &first_line);
 
+	test_maps_tearing_from_remap(maps_fd, mod_info, &page1, &page2,
+				     &last_line, &first_line);
+
 	stop_vma_modifier(mod_info);
 
 	free(page2.data);
_

Patches currently in -mm which might be from surenb@google.com are

selftests-proc-add-proc-pid-maps-tearing-from-vma-split-test.patch
selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-resizing.patch
selftests-proc-extend-proc-pid-maps-tearing-test-to-include-vma-remapping.patch
selftests-proc-test-procmap_query-ioctl-while-vma-is-concurrently-modified.patch
selftests-proc-add-verbose-more-for-tests-to-facilitate-debugging.patch
fs-proc-task_mmu-remove-conversion-of-seq_file-position-to-unsigned.patch
fs-proc-task_mmu-read-proc-pid-maps-under-per-vma-lock.patch
fs-proc-task_mmu-execute-procmap_query-ioctl-under-per-vma-locks.patch