FAILED: patch "[PATCH] bpf: Disable preemption in bpf_get_stackid" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-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 <stable@vger.kernel.org>.

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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 15f1bd8574662f1b7b26aaa2e23ebf4066f0117d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090347-bodacious-studio-93ee@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 15f1bd8574662f1b7b26aaa2e23ebf4066f0117d Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@kernel.org>
Date: Mon, 3 Aug 2026 23:01:42 +0200
Subject: [PATCH] bpf: Disable preemption in bpf_get_stackid

The get_perf_callchain call needs disabled preemption plus we need
it disabled as long as we access its returned trace entries buffer.

Note the bpf_get_stackid_pe function is executed already with
preemption disabled.

Fixes: d5a3b1f69186 ("bpf: introduce BPF_MAP_TYPE_STACK_TRACE")
Reported-by: Tao Chen <chen.dylane@linux.dev>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/bpf/20260803210149.296496-6-jolsa@kernel.org

Closes: https://lore.kernel.org/bpf/20260206090653.1336687-2-chen.dylane@linux.dev/

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 3ee0034daf52..5b18d728f4b8 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -632,20 +632,22 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 		return -EINVAL;
 
 	max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
-	trace = get_perf_callchain(regs, kernel, user, max_depth,
-				   false, false, 0);
 
-	if (unlikely(!trace))
-		/* couldn't fetch the stack trace */
-		return -EFAULT;
+	scoped_guard(preempt) {
+		trace = get_perf_callchain(regs, kernel, user, max_depth,
+					   false, false, 0);
+		if (unlikely(!trace))
+			/* couldn't fetch the stack trace */
+			return -EFAULT;
 
-	err = stackid_fastpath(&stackid, map, trace, flags);
-	if (err != -ENOENT)
-		return err;
+		err = stackid_fastpath(&stackid, map, trace, flags);
+		if (err != -ENOENT)
+			return err;
 
-	new_bucket = stackid_new_bucket(&stackid, map);
-	if (!new_bucket)
-		return -ENOMEM;
+		new_bucket = stackid_new_bucket(&stackid, map);
+		if (!new_bucket)
+			return -ENOMEM;
+	}
 
 	return stackid_install(&stackid, map, new_bucket, flags);
 }