linux-kernel - [PATCH] bcachefs: ioctl: avoid stack overflow warning

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Message-Id: <20250610092413.2640349-1-arnd@kernel.org>
Date: Tue, 10 Jun 2025 11:24:04 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
	Nathan Chancellor <nathan@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Thomas Bertschinger <tahbertschinger@...il.com>,
	linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] bcachefs: ioctl: avoid stack overflow warning

From: Arnd Bergmann <arnd@...db.de>

Multiple ioctl handlers individually use a lot of stack space, and clang chooses
to inline them into the bch2_fs_ioctl() function, blowing through the warning
limit:

fs/bcachefs/chardev.c:655:6: error: stack frame size (1032) exceeds limit (1024) in 'bch2_fs_ioctl' [-Werror,-Wframe-larger-than]
  655 | long bch2_fs_ioctl(struct bch_fs *c, unsigned cmd, void __user *arg)

By marking the largest two of them as noinline_for_stack, no indidual code path
ends up using this much, which avoids the warning and reduces the possible
total stack usage in the ioctl handler.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/bcachefs/chardev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
index 2d38466eddfd..fde3c2380e28 100644
--- a/fs/bcachefs/chardev.c
+++ b/fs/bcachefs/chardev.c
@@ -399,7 +399,7 @@ static long bch2_ioctl_data(struct bch_fs *c,
 	return ret;
 }
 
-static long bch2_ioctl_fs_usage(struct bch_fs *c,
+static noinline_for_stack long bch2_ioctl_fs_usage(struct bch_fs *c,
 				struct bch_ioctl_fs_usage __user *user_arg)
 {
 	struct bch_ioctl_fs_usage arg = {};
@@ -469,7 +469,7 @@ static long bch2_ioctl_query_accounting(struct bch_fs *c,
 }
 
 /* obsolete, didn't allow for new data types: */
-static long bch2_ioctl_dev_usage(struct bch_fs *c,
+static noinline_for_stack long bch2_ioctl_dev_usage(struct bch_fs *c,
 				 struct bch_ioctl_dev_usage __user *user_arg)
 {
 	struct bch_ioctl_dev_usage arg;
-- 
2.39.5