To: "Bryan O'Sullivan" <bos@pathscale.com>
Cc: rolandd@cisco.com, gregkh@suse.de, akpm@osdl.org, davem@davemloft.net,
       linux-kernel@vger.kernel.org, openib-general@openib.org
Subject: Re: [PATCH 9 of 20] ipath - char devices for diagnostics and lightweight subnet management
References: <eac2ad3017b5f160d24c.1141922822@localhost.localdomain>
From: Roland Dreier <rdreier@cisco.com>
Date: Thu, 09 Mar 2006 15:24:13 -0800
In-Reply-To: <eac2ad3017b5f160d24c.1141922822@localhost.localdomain> (Bryan O'Sullivan's message of "Thu,  9 Mar 2006 08:47:02 -0800")
Message-ID: <adad5gvfbhe.fsf@cisco.com>
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 > +static int ipath_sma_open(struct inode *in, struct file *fp)
 > +{
 > +	int s;
 > +
 > +	if (ipath_sma_alive) {
 > +		ipath_dbg("SMA already running (pid %u), failing\n",
 > +			  ipath_sma_alive);
 > +		return -EBUSY;
 > +	}
 > +
 > +	for (s = 0; s < atomic_read(&ipath_max); s++) {
 > +		struct ipath_devdata *dd = ipath_lookup(s);
 > +		/* we need at least one infinipath device to be initialized. */
 > +		if (dd && dd->ipath_flags & IPATH_INITTED) {
 > +			ipath_sma_alive = current->pid;

It seems there's a window here where two processes can both pass the
if (ipath_sma_alive) test and then proceed to step on each other.

 - R.
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