lkml.org 
[lkml]   [2009]   [Jul]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Fix blktrace unaligned memory access
Jens Axboe wrote:
> Hi,
>
> It seems that relay_reserve() (or the ring_buffer_event_data(), that one
> still needs some love) can return unaligned memory, there's no way
> around that when you have pdu lengths that aren't a nice size. This can
> cause unaligned access warnings on platforms that care about alignment.
>

Seems relay_reserve() does nothing for alignment..On the other hand,
ring_buffer_event_data() returns a ptr which is 32bit-aligned, but
this still means it can cause unaligned accesses on 64bits arch, while
I think it's fixable in ring buffer, it's certainly not an easy job.

> This is an RFC, perhaps we can fix this in some other way. This one takes
> the simple approach, use an on-stack copy and memcpy() that to the
> destination.
>

or get_unaligned() ?

> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 39af8af..9aba4ec 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -62,7 +62,7 @@ static void blk_unregister_tracepoints(void);
> static void trace_note(struct blk_trace *bt, pid_t pid, int action,
> const void *data, size_t len)
> {
> - struct blk_io_trace *t;
> + struct blk_io_trace *ptr, __t, *t = &__t;
> struct ring_buffer_event *event = NULL;
> int pc = 0;
> int cpu = smp_processor_id();
> @@ -75,15 +75,15 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
> 0, pc);
> if (!event)
> return;
> - t = ring_buffer_event_data(event);
> + ptr = t = ring_buffer_event_data(event);
> goto record_it;
> }
>
> if (!bt->rchan)
> return;
>
> - t = relay_reserve(bt->rchan, sizeof(*t) + len);
> - if (t) {
> + ptr = relay_reserve(bt->rchan, sizeof(*t) + len);
> + if (ptr) {
> t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
> t->time = ktime_to_ns(ktime_get());
> record_it:
> @@ -92,7 +92,9 @@ record_it:
> t->pid = pid;
> t->cpu = cpu;
> t->pdu_len = len;
> - memcpy((void *) t + sizeof(*t), data, len);
> + if (t == &__t)
> + memcpy(ptr, t, sizeof(*t));
> + memcpy((void *) ptr + sizeof(*ptr), data, len);
>
> if (blk_tracer)
> trace_buffer_unlock_commit(blk_tr, event, 0, pc);
> @@ -178,7 +180,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
> {
> struct task_struct *tsk = current;
> struct ring_buffer_event *event = NULL;
> - struct blk_io_trace *t;
> + struct blk_io_trace *ptr, __t, *t = &__t;
> unsigned long flags = 0;
> unsigned long *sequence;
> pid_t pid;
> @@ -209,7 +211,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
> 0, pc);
> if (!event)
> return;
> - t = ring_buffer_event_data(event);
> + ptr = t = ring_buffer_event_data(event);
> goto record_it;
> }
>
> @@ -223,8 +225,8 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
> if (unlikely(tsk->btrace_seq != blktrace_seq))
> trace_note_tsk(bt, tsk);
>
> - t = relay_reserve(bt->rchan, sizeof(*t) + pdu_len);
> - if (t) {
> + ptr = relay_reserve(bt->rchan, sizeof(*ptr) + pdu_len);
> + if (ptr) {
> sequence = per_cpu_ptr(bt->sequence, cpu);
>
> t->magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION;
> @@ -247,8 +249,10 @@ record_it:
> t->error = error;
> t->pdu_len = pdu_len;
>
> + if (t == &__t)
> + memcpy(ptr, t, sizeof(*t));
> if (pdu_len)
> - memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
> + memcpy((void *) ptr + sizeof(*ptr), pdu_data, pdu_len);
>
> if (blk_tracer) {
> trace_buffer_unlock_commit(blk_tr, event, 0, pc);
>



\
 
 \ /
  Last update: 2009-07-10 11:11    [W:0.050 / U:1.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site