Messages in this thread | | | Date | Fri, 10 Jul 2009 17:07:54 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] Fix blktrace unaligned memory access |
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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); >
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