From 7030017752437cebc3ec5590735bd89ead1e4cb8 Mon Sep 17 00:00:00 2001 From: "Luis R. Rodriguez" Date: Wed, 6 Aug 2014 16:08:49 -0700 Subject: [PATCH] printk: make dynamic kernel ring buffer alignment explicit We have to consider alignment for the ring buffer both for the default static size, and then also for when an dynamic allocation is made when the log_buf_len=n kernel parameter is passed to set the size specifically to a size larger than the default size set by the architecture through CONFIG_LOG_BUF_SHIFT. The default static kernel ring buffer can be aligned properly if architectures set CONFIG_LOG_BUF_SHIFT properly, we provide ranges for the size though so even if CONFIG_LOG_BUF_SHIFT has a sensible aligned value it can be reduced to a non aligned value. Commit 6ebb017de9 ("printk: Fix alignment of buf causing crash on ARM EABI") by Andrew Lunn ensures the static buffer is always aligned and the decision of alignment is done by the compiler by using __alignof__(struct log). When log_buf_len=n is used we allocate the ring buffer dynamically. Dynamic allocation varies, for the early allocation called before setup_arch() memblock_virt_alloc() requests a page aligment and for the default kernel allocation memblock_virt_alloc_nopanic() requests no special alignment, which in turn ends up aligning the allocation to SMP_CACHE_BYTES, which is L1 cache aligned. Since we already have the required alignment for the kernel ring buffer though we can do better and request explicit alignment for LOG_ALIGN. This does that to be safe and make dynamic allocation alignment explicit. Signed-off-by: Luis R. Rodriguez Tested-by: Petr Mladek Acked-by: Petr Mladek Cc: Andrew Lunn Cc: Stephen Warren Cc: Greg Kroah-Hartman Cc: Michal Hocko Cc: Petr Mladek Cc: Joe Perches Cc: Arun KS Cc: Kees Cook Cc: Davidlohr Bueso Cc: Chris Metcalf Cc: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/printk/printk.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 13e839dbca07..6f598f92f2a1 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -853,9 +853,10 @@ void __init setup_log_buf(int early) if (early) { new_log_buf = - memblock_virt_alloc(new_log_buf_len, PAGE_SIZE); + memblock_virt_alloc(new_log_buf_len, LOG_ALIGN); } else { - new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len, 0); + new_log_buf = memblock_virt_alloc_nopanic(new_log_buf_len, + LOG_ALIGN); } if (unlikely(!new_log_buf)) { -- 2.20.1