linux-kernel - Re: [PATCH] iwlwifi: mvm: no need to check return value of debugfs

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Message-ID: <20190327012600.GA3649@kroah.com>
Date:   Wed, 27 Mar 2019 10:26:00 +0900
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH] iwlwifi: mvm: no need to check return value of
 debugfs_create functions

On Tue, Mar 26, 2019 at 04:55:54PM -0700, Laura Abbott wrote:
> On 1/22/19 7:21 AM, Greg Kroah-Hartman wrote:
> > diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c b/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> > index 33b0af24a537..c52cdc538678 100644
> > --- a/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> > +++ b/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> > @@ -1446,9 +1446,8 @@ static ssize_t iwl_dbgfs_quota_min_read(struct file *file,
> >   #define MVM_DEBUGFS_READ_WRITE_FILE_OPS(name, bufsz) \
> >   	_MVM_DEBUGFS_READ_WRITE_FILE_OPS(name, bufsz, struct ieee80211_vif)
> >   #define MVM_DEBUGFS_ADD_FILE_VIF(name, parent, mode) do {		\
> > -		if (!debugfs_create_file(#name, mode, parent, vif,	\
> > -					 &iwl_dbgfs_##name##_ops))	\
> > -			goto err;					\
> > +		debugfs_create_file(#name, mode, parent, vif,		\
> > +				    &iwl_dbgfs_##name##_ops);		\
> >   	} while (0)
> >   MVM_DEBUGFS_READ_FILE_OPS(mac_params);
> > @@ -1483,12 +1482,6 @@ void iwl_mvm_vif_dbgfs_register(struct iwl_mvm *mvm, struct ieee80211_vif *vif)
> >   	mvmvif->dbgfs_dir = debugfs_create_dir("iwlmvm", dbgfs_dir);
> > -	if (!mvmvif->dbgfs_dir) {
> > -		IWL_ERR(mvm, "Failed to create debugfs directory under %pd\n",
> > -			dbgfs_dir);
> > -		return;
> > -	}
> > -
> >   	if (iwlmvm_mod_params.power_scheme != IWL_POWER_SCHEME_CAM &&
> >   	    ((vif->type == NL80211_IFTYPE_STATION && !vif->p2p) ||
> >   	     (vif->type == NL80211_IFTYPE_STATION && vif->p2p)))
> > @@ -1537,12 +1530,6 @@ void iwl_mvm_vif_dbgfs_register(struct iwl_mvm *mvm, struct ieee80211_vif *vif)
> >   	mvmvif->dbgfs_slink = debugfs_create_symlink(dbgfs_dir->d_name.name,
> >   						     mvm->debugfs_dir, buf);
> > -	if (!mvmvif->dbgfs_slink)
> > -		IWL_ERR(mvm, "Can't create debugfs symbolic link under %pd\n",
> > -			dbgfs_dir);
> > -	return;
> > -err:
> > -	IWL_ERR(mvm, "Can't create debugfs entity\n");
> >   }
> 
> Fedora got a bug report https://bugzilla.redhat.com/show_bug.cgi?id=1691034
> of a crash with 5.0 and the user did a bisect which pointed to ff9fb72bc077
> ("debugfs: return error values, not NULL") because the error checking is
> no longer correct in this driver.
> 
> Based on https://patchwork.kernel.org/patch/10865839/, it looks like
> this is supposed to go in for 5.2 but this needs to go in now as
> the error checking is currently broken without it. Can this get queued
> for Linus so we can get it in 5.0 stable?

That's odd, I can't see how the error checking is wrong here.  If the
directory is not created, an error will be returned, which should be
able to be handled by debugfs_create_file().

So with this patch does the error go away?

strange,

greg k-h