linux-kernel - drivers/gpu/drm/nouveau/nouveau_dp.c:237 nouveau_dp_irq() warn: variable dereferenced before check 'outp' (see line 232)

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Message-ID: <202212300411.7i7D8MbF-lkp@intel.com>
Date:   Tue, 3 Jan 2023 11:02:01 +0300
From:   Dan Carpenter <error27@...il.com>
To:     oe-kbuild@...ts.linux.dev, Ben Skeggs <bskeggs@...hat.com>
Cc:     lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Lyude Paul <lyude@...hat.com>
Subject: drivers/gpu/drm/nouveau/nouveau_dp.c:237 nouveau_dp_irq() warn:
 variable dereferenced before check 'outp' (see line 232)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   2258c2dc850b8605cb66b3383e50b9dddd1c6580
commit: 773eb04d14a11552b2c3953097ed09cde2ab4831 drm/nouveau/disp: expose conn event class
config: ia64-randconfig-m031-20221229
compiler: ia64-linux-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <error27@...il.com>

smatch warnings:
drivers/gpu/drm/nouveau/nouveau_dp.c:237 nouveau_dp_irq() warn: variable dereferenced before check 'outp' (see line 232)

vim +/outp +237 drivers/gpu/drm/nouveau/nouveau_dp.c

773eb04d14a115 Ben Skeggs 2022-06-01  225  void
773eb04d14a115 Ben Skeggs 2022-06-01  226  nouveau_dp_irq(struct work_struct *work)
a0922278f83eae Lyude Paul 2020-08-26  227  {
773eb04d14a115 Ben Skeggs 2022-06-01  228  	struct nouveau_connector *nv_connector =
773eb04d14a115 Ben Skeggs 2022-06-01  229  		container_of(work, typeof(*nv_connector), irq_work);
a0922278f83eae Lyude Paul 2020-08-26  230  	struct drm_connector *connector = &nv_connector->base;
a0922278f83eae Lyude Paul 2020-08-26  231  	struct nouveau_encoder *outp = find_encoder(connector, DCB_OUTPUT_DP);
773eb04d14a115 Ben Skeggs 2022-06-01 @232  	struct nouveau_drm *drm = nouveau_drm(outp->base.base.dev);
                                                                                      ^^^^^^
Dereference.

a0922278f83eae Lyude Paul 2020-08-26  233  	struct nv50_mstm *mstm;
016dacb60e6d4b Ben Skeggs 2022-06-01  234  	u64 hpd = 0;
a4efad354cf1b9 Lyude Paul 2020-08-26  235  	int ret;
a0922278f83eae Lyude Paul 2020-08-26  236  
a0922278f83eae Lyude Paul 2020-08-26 @237  	if (!outp)
                                                     ^^^^
Checked too late.

a0922278f83eae Lyude Paul 2020-08-26  238  		return;
a0922278f83eae Lyude Paul 2020-08-26  239  
a0922278f83eae Lyude Paul 2020-08-26  240  	mstm = outp->dp.mstm;
a0922278f83eae Lyude Paul 2020-08-26  241  	NV_DEBUG(drm, "service %s\n", connector->name);
a0922278f83eae Lyude Paul 2020-08-26  242  
a0922278f83eae Lyude Paul 2020-08-26  243  	mutex_lock(&outp->dp.hpd_irq_lock);
a0922278f83eae Lyude Paul 2020-08-26  244  
a0922278f83eae Lyude Paul 2020-08-26  245  	if (mstm && mstm->is_mst) {
a0922278f83eae Lyude Paul 2020-08-26  246  		if (!nv50_mstm_service(drm, nv_connector, mstm))
773eb04d14a115 Ben Skeggs 2022-06-01  247  			hpd |= NVIF_CONN_EVENT_V0_UNPLUG;
a0922278f83eae Lyude Paul 2020-08-26  248  	} else {
a0922278f83eae Lyude Paul 2020-08-26  249  		drm_dp_cec_irq(&nv_connector->aux);
a4efad354cf1b9 Lyude Paul 2020-08-26  250  
a4efad354cf1b9 Lyude Paul 2020-08-26  251  		if (nouveau_dp_has_sink_count(connector, outp)) {
a4efad354cf1b9 Lyude Paul 2020-08-26  252  			ret = drm_dp_read_sink_count(&nv_connector->aux);
a4efad354cf1b9 Lyude Paul 2020-08-26  253  			if (ret != outp->dp.sink_count)
773eb04d14a115 Ben Skeggs 2022-06-01  254  				hpd |= NVIF_CONN_EVENT_V0_PLUG;
a4efad354cf1b9 Lyude Paul 2020-08-26  255  			if (ret >= 0)
a4efad354cf1b9 Lyude Paul 2020-08-26  256  				outp->dp.sink_count = ret;
a4efad354cf1b9 Lyude Paul 2020-08-26  257  		}
a0922278f83eae Lyude Paul 2020-08-26  258  	}
a0922278f83eae Lyude Paul 2020-08-26  259  
a0922278f83eae Lyude Paul 2020-08-26  260  	mutex_unlock(&outp->dp.hpd_irq_lock);
a4efad354cf1b9 Lyude Paul 2020-08-26  261  
773eb04d14a115 Ben Skeggs 2022-06-01  262  	nouveau_connector_hpd(nv_connector, NVIF_CONN_EVENT_V0_IRQ | hpd);
a0922278f83eae Lyude Paul 2020-08-26  263  }

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