linux-kernel - Re: [PATCH v3 5/6] blktrace: break out of blktrace setup on concurrent calls

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Message-ID: <20200501165145.GA2085362@kroah.com>
Date:   Fri, 1 May 2020 18:51:45 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk, bvanassche@....org,
        rostedt@...dmis.org, mingo@...hat.com, jack@...e.cz,
        ming.lei@...hat.com, nstange@...e.de, akpm@...ux-foundation.org,
        mhocko@...e.com, yukuai3@...wei.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/6] blktrace: break out of blktrace setup on
 concurrent calls

On Fri, May 01, 2020 at 03:06:26PM +0000, Luis Chamberlain wrote:
> On Wed, Apr 29, 2020 at 11:49:37AM +0200, Greg KH wrote:
> > On Wed, Apr 29, 2020 at 07:46:26AM +0000, Luis Chamberlain wrote:
> > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> > > index 5c52976bd762..383045f67cb8 100644
> > > --- a/kernel/trace/blktrace.c
> > > +++ b/kernel/trace/blktrace.c
> > > @@ -516,6 +518,11 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> > >  	 */
> > >  	strreplace(buts->name, '/', '_');
> > >  
> > > +	if (q->blk_trace) {
> > > +		pr_warn("Concurrent blktraces are not allowed\n");
> > > +		return -EBUSY;
> > 
> > You have access to a block device here, please use dev_warn() instead
> > here for that, that makes it obvious as to what device a "concurrent
> > blktrace" was attempted for.
> 
> The block device may be empty, one example is for scsi-generic, but I'll
> use buts->name.

That's fine, give us a chance to know what went wrong, your line as is
does not do that :(

thanks,

greg k-h