FAILED: patch "[PATCH] mm/damon/vaddr: fix issue in damon_va_evenly_split_region()" failed to apply to 6.6-stable tree

[email protected]

author maintainer

2024-12-06 10:16 UTC #0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f3c7a1ede435e2e45177d7a490a85fb0a0ec96d1
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024120622-postcard-cringe-b986@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f3c7a1ede435e2e45177d7a490a85fb0a0ec96d1 Mon Sep 17 00:00:00 2001
From: Zheng Yejian <[email protected]>
Date: Tue, 22 Oct 2024 16:39:26 +0800
Subject: [PATCH] mm/damon/vaddr: fix issue in damon_va_evenly_split_region()

Patch series "mm/damon/vaddr: Fix issue in
damon_va_evenly_split_region()". v2.

According to the logic of damon_va_evenly_split_region(), currently following split case would not meet the expectation:

Suppose DAMON_MIN_REGION=0x1000,
Case: Split [0x0, 0x3000) into 2 pieces, then the result would be
acutually 3 regions:
[0x0, 0x1000), [0x1000, 0x2000), [0x2000, 0x3000)
but NOT the expected 2 regions:
[0x0, 0x1000), [0x1000, 0x3000) !!!

The root cause is that when calculating size of each split piece in damon_va_evenly_split_region():

sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);

both the dividing and the ALIGN_DOWN may cause loss of precision, then each time split one piece of size 'sz_piece' from origin 'start' to 'end' would cause more pieces are split out than expected!!!

To fix it, count for each piece split and make sure no more than 'nr_pieces'. In addition, add above case into damon_test_split_evenly().

And add 'nr_piece == 1' check in damon_va_evenly_split_region() for better code readability and add a corresponding kunit testcase.

This patch (of 2):

According to the logic of damon_va_evenly_split_region(), currently following split case would not meet the expectation:

Suppose DAMON_MIN_REGION=0x1000,
Case: Split [0x0, 0x3000) into 2 pieces, then the result would be
acutually 3 regions:
[0x0, 0x1000), [0x1000, 0x2000), [0x2000, 0x3000)
but NOT the expected 2 regions:
[0x0, 0x1000), [0x1000, 0x3000) !!!

The root cause is that when calculating size of each split piece in damon_va_evenly_split_region():

sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);

both the dividing and the ALIGN_DOWN may cause loss of precision, then each time split one piece of size 'sz_piece' from origin 'start' to 'end' would cause more pieces are split out than expected!!!

To fix it, count for each piece split and make sure no more than 'nr_pieces'. In addition, add above case into damon_test_split_evenly().

After this patch, damon-operations test passed:

 # ./tools/testing/kunit/kunit.py run damon-operations
 [...]
 ============== damon-operations (6 subtests) ===============
 [PASSED] damon_test_three_regions_in_vmas
 [PASSED] damon_test_apply_three_regions1
 [PASSED] damon_test_apply_three_regions2
 [PASSED] damon_test_apply_three_regions3
 [PASSED] damon_test_apply_three_regions4
 [PASSED] damon_test_split_evenly
 ================ [PASSED] damon-operations =================

Link https://lkml.kernel.org/r/[email protected] open here

Fixes 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces")

Signed-off-by Zheng Yejian <[email protected]>

Reviewed-by SeongJae Park <[email protected]>

Cc Fernand Sieber <[email protected]>

Cc Leonard Foerster <[email protected]>

Cc Shakeel Butt <[email protected]>

Cc Ye Weihua <[email protected]>

Cc <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

mm/damon/tests/vaddr-kunit.h +1 -0

index 3dad8dfd9005..fcdccb614fd8 100644
@@ -300,6 +300,7 @@ static void damon_test_split_evenly(struct kunit *test)
 	damon_test_split_evenly_fail(test, 0, 100, 0);
 	damon_test_split_evenly_succ(test, 0, 100, 10);
 	damon_test_split_evenly_succ(test, 5, 59, 5);
+	damon_test_split_evenly_succ(test, 0, 3, 2);
 	damon_test_split_evenly_fail(test, 5, 6, 2);
 }

mm/damon/vaddr.c +2 -2

index 821990d0141a..86f612fbf886 100644
@@ -67,6 +67,7 @@ static int damon_va_evenly_split_region(struct damon_target *t,
 	unsigned long sz_orig, sz_piece, orig_end;
 	struct damon_region *n = NULL, *next;
 	unsigned long start;
+	unsigned int i;
 
 	if (!r || !nr_pieces)
 		return -EINVAL;

@@ -80,8 +81,7 @@ static int damon_va_evenly_split_region(struct damon_target *t,
 
 	r->ar.end = r->ar.start + sz_piece;
 	next = damon_next_region(r);
-	for (start = r->ar.end; start + sz_piece <= orig_end;
-			start += sz_piece) {
+	for (start = r->ar.end, i = 1; i < nr_pieces; start += sz_piece, i++) {
 		n = damon_new_region(start, start + sz_piece);
 		if (!n)
 			return -ENOMEM;

SeongJae Park

maintainer

2024-12-06 17:34 UTC #1 lore raw

Quoted 6 lines · On Fri, 06 Dec 2024 11:16:22 +0100 <[email protected]> wrote:

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Quoted 6 lines

To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD
git cherry-pick -x f3c7a1ede435e2e45177d7a490a85fb0a0ec96d1
# <resolve conflicts, build, test, etc.>

I tried this on the latest linux-6.6.y (v6.6.63), and the cherry-pick didn't reproduce the conflict as below.

    $ git checkout stable/linux-6.6.y
    [...]
    HEAD is now at bff3e13adb72 Linux 6.6.63
    damian@damian:~/linux$ git cherry-pick -x f3c7a1ede435e2e45177d7a490a85fb0a0ec96d1
    Auto-merging mm/damon/vaddr-test.h
    Auto-merging mm/damon/vaddr.c
    [detached HEAD 072adde8b33a] mm/damon/vaddr: fix issue in damon_va_evenly_split_region()
     Author: Zheng Yejian <[email protected]>
     Date: Tue Oct 22 16:39:26 2024 +0800
     2 files changed, 3 insertions(+), 2 deletions(-)

mm/damon/tests/vaddr-kunit.h was originally mm/damon/vaddr-test.h, and the path conversion patch is not on the linux-6.6.y tree. In my case, seems git was able to know the path change and finish cherry-pick successfully was maybe it didn't work on your setup for some reason?

Anyway, I'll post the successfully cherry-picked one as a reply to this soon.

Thanks,
SJ

SeongJae Park

maintainer

2024-12-06 17:37 UTC #2 lore raw

PATCH 1/1 mm/damon/vaddr: fix issue in damon_va_evenly_split_region()

From: Zheng Yejian <[email protected]>