On Wed, Jun 11 2008, Carl Henrik Lunde wrote:
> On Fri, May 30, 2008 at 13:44, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
> > On Fri, May 30 2008, Carl Henrik Lunde wrote:
> >> Hi,
> >>
> >> Can you review this patch? I'm new to locking in the Linux kernel
> >> so I may be misssing something.
> >>
> >> I think we must disable IRQs between relay_reserve and initializing
> >> the data; consider the following scenario where task 1 and task 2
> >> runs on the same CPU:
> >>
> >> task 1: trace_note_message task 2: interrupt userspace (blktrace)
> >> -------------------------- ----------------- --------------------
> >> __trace_note_message read(relay)
> >> relay_reserve <blocks ...>
> >> <interrupted: I/O completion>
> >>
> >> __blk_add_trace
> >> relay_reserve
> >> <buffers switched,
> >> wake user>
> >> <reads uninitialized
> >> trace_note_message>
> >> <done>
> >> <runs again>
> >> memcpy() - too late
> >>
> >> --
> >> Carl Henrik
> >
> >> From 30fce97a2d7c02ba265eceed59592dbdc9c34f26 Mon Sep 17 00:00:00 2001
> >> From: Carl Henrik Lunde <chlunde@xxxxxxxxxxx>
> >> Date: Fri, 30 May 2008 12:57:47 +0200
> >> Subject: [PATCH] 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@xxxxxxxxxxx>
> >> ---
> >> block/blktrace.c | 10 ++++------
> >> 1 files changed, 4 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/block/blktrace.c b/block/blktrace.c
> >> index 7ae87cc..8d3a277 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);
> >
> > Good spotting, applied! Thanks.
>
> Hmm, applied where?
Still local, I'll get it pushed out for 2.6.26 final for sure.
--
Jens Axboe
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