FAILED: patch "[PATCH] ARM: 9472/1: fix race condition on PG_dcache_clean in" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 75f9a484e817adea211c73f89ed938a2b2f90953
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026050413-consoling-coauthor-12a3@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 75f9a484e817adea211c73f89ed938a2b2f90953 Mon Sep 17 00:00:00 2001
From: Brian Ruley <[email protected]>
Date: Wed, 15 Apr 2026 18:12:48 +0100
Subject: [PATCH] ARM: 9472/1: fix race condition on PG_dcache_clean in
__sync_icache_dcache()

This bug was already discovered and fixed for arm64 in commit 588a513d3425 ("arm64: Fix race condition on PG_dcache_clean in __sync_icache_dcache()").

Verified with added instrumentation to track dcache flushes in a ring buffer, as shown by the (distilled) output:

kernel: SIGILL at b6b80ac0 cpu 1 pid 32663 linux_pte=8eff659f

          hw_pte=8eff6e7e young=1 exec=1

kernel: dcache flush START cpu0 pfn=8eff6 ts=48629557020154
kernel: dcache flush SKIPPED cpu1 pfn=8eff6 ts=48629557020154
kernel: dcache flush FINISH cpu0 pfn=8eff6 ts=48629557036154
audisp-syslog: comm="journalctl" exe="/usr/bin/journalctl" sig=4 [...]

Discussions in the mailing list mentioned that arch/arm is also affected but the fix was never applied to it [1][2]. Apply the change now, since the race condition can cause sporadic SIGILL's and SEGV's especially while under high memory pressure.

index 19470d938b23..4d7ef5cc36b6 100644
@@ -304,8 +304,10 @@ void __sync_icache_dcache(pte_t pteval)
 	else
 		mapping = NULL;
 
-	if (!test_and_set_bit(PG_dcache_clean, &folio->flags.f))
+	if (!test_bit(PG_dcache_clean, &folio->flags.f)) {
 		__flush_dcache_folio(mapping, folio);
+		set_bit(PG_dcache_clean, &folio->flags.f);
+	}
 
 	if (pte_exec(pteval))
 		__flush_icache_all();