fs: sysfs_emit_at: Remove PAGE_SIZE alignment check

From: Eric Biggers <[email protected]>

[No upstream commit because this fixes a bug in a backport.]

Before upstream commit 59bb47985c1d ("mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)") which went into v5.4, kmalloc did *not* always guarantee that PAGE_SIZE allocations are PAGE_SIZE-aligned.

Upstream commit 2efc459d06f1 ("sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output") added two WARN()s that trigger when PAGE_SIZE allocations are not PAGE_SIZE-aligned. This was backported to old kernels that don't guarantee PAGE_SIZE alignment.

Commit 10ddfb495232 ("fs: sysfs_emit: Remove PAGE_SIZE alignment check") in 4.19.y, and its equivalent in 4.14.y and 4.9.y, tried to fix this bug. However, only it handled sysfs_emit(), not sysfs_emit_at().

Fix it in sysfs_emit_at() too.

A reproducer is to build the kernel with the following options:

CONFIG_SLUB=y
CONFIG_SLUB_DEBUG=y
CONFIG_SLUB_DEBUG_ON=y
CONFIG_PM=y
CONFIG_SUSPEND=y
CONFIG_PM_WAKELOCKS=y

Then run:

	echo foo > /sys/power/wake_lock && cat /sys/power/wake_lock

---
 fs/sysfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index c41e7f51150fc..cef9a469f73a8 100644
@@ -592,7 +592,7 @@ int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
 	va_list args;
 	int len;
 
-	if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
+	if (WARN(!buf || at < 0 || at >= PAGE_SIZE,
 		 "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
 		return 0;
 

2.39.2