+ selftests-add-selftests-for-cachestat-fix-2.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: selftests-add-selftests-for-cachestat-fix-2
has been added to the -mm mm-unstable branch.  Its filename is
     selftests-add-selftests-for-cachestat-fix-2.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-add-selftests-for-cachestat-fix-2.patch

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

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

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------------------------------------------------------
From: Michael Ellerman <mpe@ellerman.id.au>
Subject: selftests-add-selftests-for-cachestat-fix-2
Date: Thu, 11 May 2023 13:21:28 +1000

On kernels with 64K pages (powerpc at least), this tries to allocate
64MB on the stack which segfaults.

Allocating data with malloc avoids the problem and allows the test to
pass.

Link: https://lkml.kernel.org/r/877ctfa6yv.fsf@mail.lhotse
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Brian Foster <bfoster@redhat.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/cachestat/test_cachestat.c |   69 ++++++-----
 1 file changed, 40 insertions(+), 29 deletions(-)

--- a/tools/testing/selftests/cachestat/test_cachestat.c~selftests-add-selftests-for-cachestat-fix-2
+++ a/tools/testing/selftests/cachestat/test_cachestat.c
@@ -31,48 +31,59 @@ void print_cachestat(struct cachestat *c
 
 bool write_exactly(int fd, size_t filesize)
 {
-	char data[filesize];
-	bool ret = true;
 	int random_fd = open("/dev/urandom", O_RDONLY);
+	char *cursor, *data;
+	int remained;
+	bool ret;
 
 	if (random_fd < 0) {
 		ksft_print_msg("Unable to access urandom.\n");
 		ret = false;
 		goto out;
-	} else {
-		int remained = filesize;
-		char *cursor = data;
-
-		while (remained) {
-			ssize_t read_len = read(random_fd, cursor, remained);
-
-			if (read_len <= 0) {
-				ksft_print_msg("Unable to read from urandom.\n");
-				ret = false;
-				goto close_random_fd;
-			}
+	}
+
+	data = malloc(filesize);
+	if (!data) {
+		ksft_print_msg("Unable to allocate data.\n");
+		ret = false;
+		goto close_random_fd;
+	}
 
-			remained -= read_len;
-			cursor += read_len;
+	remained = filesize;
+	cursor = data;
+
+	while (remained) {
+		ssize_t read_len = read(random_fd, cursor, remained);
+
+		if (read_len <= 0) {
+			ksft_print_msg("Unable to read from urandom.\n");
+			ret = false;
+			goto out_free_data;
 		}
 
-		/* write random data to fd */
-		remained = filesize;
-		cursor = data;
-		while (remained) {
-			ssize_t write_len = write(fd, cursor, remained);
-
-			if (write_len <= 0) {
-				ksft_print_msg("Unable write random data to file.\n");
-				ret = false;
-				goto close_random_fd;
-			}
+		remained -= read_len;
+		cursor += read_len;
+	}
 
-			remained -= write_len;
-			cursor += write_len;
+	/* write random data to fd */
+	remained = filesize;
+	cursor = data;
+	while (remained) {
+		ssize_t write_len = write(fd, cursor, remained);
+
+		if (write_len <= 0) {
+			ksft_print_msg("Unable write random data to file.\n");
+			ret = false;
+			goto out_free_data;
 		}
+
+		remained -= write_len;
+		cursor += write_len;
 	}
 
+	ret = true;
+out_free_data:
+	free(data);
 close_random_fd:
 	close(random_fd);
 out:
_

Patches currently in -mm which might be from mpe@ellerman.id.au are

mm-kfence-fix-false-positives-on-big-endian.patch
selftests-add-selftests-for-cachestat-fix-2.patch