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>

diff --git a/block/blktrace.c b/block/blktrace.c
index 7ae87cc..8d3a277 100644 (file)
--- 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);