linux-kernel - [PATCH] tty: hvc: don't allocate a buffer for console print on stack

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Message-Id: <1487364165-21882-1-git-send-email-jan.dakinevich@gmail.com>
Date:   Fri, 17 Feb 2017 23:42:45 +0300
From:   Jan Dakinevich <jan.dakinevich@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Jan Dakinevich <jan.dakinevich@...il.com>,
        Peter Hurley <peter@...leysoftware.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Arnd Bergmann <arnd@...db.de>, Amit Shah <amit@...nel.org>,
        virtualization@...ts.linux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH] tty: hvc: don't allocate a buffer for console print on stack

The buffer is used by virtio console driver as DMA buffer. Since v4.9
(if VMAP_STACK is enabled) we shouldn't use the stack for DMA.

Signed-off-by: Jan Dakinevich <jan.dakinevich@...il.com>
---
 drivers/tty/hvc/hvc_console.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 9b5c0fb..1ce6aaf 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -143,10 +143,15 @@ static struct hvc_struct *hvc_get_by_index(int index)
 static void hvc_console_print(struct console *co, const char *b,
 			      unsigned count)
 {
-	char c[N_OUTBUF] __ALIGNED__;
 	unsigned i = 0, n = 0;
 	int r, donecr = 0, index = co->index;
 
+	/*
+	 * Access to the buffer is serialized by console_sem in caller code from
+	 * kernel/printk/printk.c
+	 */
+	static char c[N_OUTBUF] __ALIGNED__;
+
 	/* Console access attempt outside of acceptable console range. */
 	if (index >= MAX_NR_HVC_CONSOLES)
 		return;
-- 
1.9.1