Messages in this thread | | | Date | Wed, 28 May 2008 23:13:51 -0700 | From | Andrew Morton <> | Subject | Re: block: make blktrace use per-cpu buffers for message notes |
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On Wed, 28 May 2008 15:59:07 GMT Linux Kernel Mailing List <linux-kernel@vger.kernel.org> wrote:
> Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=64565911cdb57c2f512a9715b985b5617402cc67 > Commit: 64565911cdb57c2f512a9715b985b5617402cc67 > Parent: 4722dc52a891ab6cb2d637ddb87233e0ce277827 > Author: Jens Axboe <jens.axboe@oracle.com> > AuthorDate: Wed May 28 14:45:33 2008 +0200 > Committer: Jens Axboe <jens.axboe@oracle.com> > CommitDate: Wed May 28 14:49:27 2008 +0200
please try to avoid merging unreviewed changes.
> block: make blktrace use per-cpu buffers for message notes > > Currently it uses a single static char array, but that risks > being corrupted when multiple users issue message notes at the > same time. Make the buffers dynamically allocated when the trace > is setup and make them per-cpu instead. > > The default max message size of 1k is also very large, the > interface is mainly for small text notes. So shrink it to 128 bytes. > > Signed-off-by: Jens Axboe <jens.axboe@oracle.com> > --- > block/blktrace.c | 15 ++++++++++++--- > include/linux/blktrace_api.h | 3 ++- > 2 files changed, 14 insertions(+), 4 deletions(-) > > diff --git a/block/blktrace.c b/block/blktrace.c > index 20e11f3..7ae87cc 100644 > --- a/block/blktrace.c > +++ b/block/blktrace.c > @@ -79,13 +79,16 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...) > { > int n; > va_list args; > - static char bt_msg_buf[BLK_TN_MAX_MSG]; > + char *buf; > > + preempt_disable(); > + buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
get_cpu()/put_cpu() is the standard way of doing this.
> @@ -172,7 +173,7 @@ extern void __trace_note_message(struct blk_trace *, const char *fmt, ...); > if (unlikely(bt)) \ > __trace_note_message(bt, fmt, ##__VA_ARGS__); \ > } while (0) > -#define BLK_TN_MAX_MSG 1024 > +#define BLK_TN_MAX_MSG 128
It seems a bit strange to do this right when we've taken this _off_ the stack. But I suppose nothing will break.
I cannot work out why 9d5f09a424a67ddb959829894efb4c71cbf6d600 ("Added in MESSAGE notes for blktraces") was -rc material.
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