Commit 70300177 authored by Luis R. Rodriguez's avatar Luis R. Rodriguez Committed by Linus Torvalds
Browse files

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 6ebb017d

("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
Signed-off-by: default avatarLuis R. Rodriguez <>
Tested-by: default avatarPetr Mladek <>
Acked-by: default avatarPetr 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: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 90a85643
......@@ -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,
if (unlikely(!new_log_buf)) {
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment