block: disable IRQs until data is written to relay channel

As we may run relay_reserve from interrupt context we must always disable
IRQs.  This is because a call to relay_reserve may expose previously written
data to use space.

Updated new message code and an old but related comment.

Signed-off-by: Carl Henrik Lunde <chlunde@ping.uio.no>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 6 deletions

diff --git a/block/blktrace.c b/block/blktrace.c
index 7ae87cc4a163..8d3a27780260 100644
--- a/block/blktrace.c
+++ b/block/blktrace.c
@@ -79,16 +79,17 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
 {
         int n;
         va_list args;
+        unsigned long flags;
         char *buf;
 
-        preempt_disable();
+        local_irq_save(flags);
         buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
         va_start(args, fmt);
         n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
         va_end(args);
 
         trace_note(bt, 0, BLK_TN_MESSAGE, buf, n);
-        preempt_enable();
+        local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(__trace_note_message);
 
@@ -158,10 +159,7 @@ void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
         /*
          * A word about the locking here - we disable interrupts to reserve
          * some space in the relay per-cpu buffer, to prevent an irq
-         * from coming in and stepping on our toes. Once reserved, it's
-         * enough to get preemption disabled to prevent read of this data
-         * before we are through filling it. get_cpu()/put_cpu() does this
-         * for us
+         * from coming in and stepping on our toes.
          */
         local_irq_save(flags);