linux-kernel - drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c:282 nvkm_chan_cctx_get() warn: inconsistent returns '&cgrp->mutex'.

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Date:   Thu, 29 Dec 2022 12:24:49 +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/nvkm/engine/fifo/chan.c:282
 nvkm_chan_cctx_get() warn: inconsistent returns '&cgrp->mutex'.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   72a85e2b0a1e1e6fb4ee51ae902730212b2de25c
commit: f48dd2936138882d7755cbbc5d9984015c75980c drm/nouveau/fifo: add new engine context tracking
config: s390-randconfig-m041-20221225
compiler: s390-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/nvkm/engine/fifo/chan.c:282 nvkm_chan_cctx_get() warn: inconsistent returns '&cgrp->mutex'.

vim +282 drivers/gpu/drm/nouveau/nvkm/engine/fifo/chan.c

f48dd293613888 Ben Skeggs 2022-06-01  241  int
f48dd293613888 Ben Skeggs 2022-06-01  242  nvkm_chan_cctx_get(struct nvkm_chan *chan, struct nvkm_engn *engn, struct nvkm_cctx **pcctx,
f48dd293613888 Ben Skeggs 2022-06-01  243  		   struct nvkm_client *client)
f48dd293613888 Ben Skeggs 2022-06-01  244  {
f48dd293613888 Ben Skeggs 2022-06-01  245  	struct nvkm_cgrp *cgrp = chan->cgrp;
f48dd293613888 Ben Skeggs 2022-06-01  246  	struct nvkm_vctx *vctx;
f48dd293613888 Ben Skeggs 2022-06-01  247  	struct nvkm_cctx *cctx;
f48dd293613888 Ben Skeggs 2022-06-01  248  	int ret;
f48dd293613888 Ben Skeggs 2022-06-01  249  
f48dd293613888 Ben Skeggs 2022-06-01  250  	/* Look for an existing channel context for this engine+VEID. */
f48dd293613888 Ben Skeggs 2022-06-01  251  	mutex_lock(&cgrp->mutex);
f48dd293613888 Ben Skeggs 2022-06-01  252  	cctx = nvkm_list_find(cctx, &chan->cctxs, head,
f48dd293613888 Ben Skeggs 2022-06-01  253  			      cctx->vctx->ectx->engn == engn && cctx->vctx->vmm == chan->vmm);
f48dd293613888 Ben Skeggs 2022-06-01  254  	if (cctx) {
f48dd293613888 Ben Skeggs 2022-06-01  255  		refcount_inc(&cctx->refs);
f48dd293613888 Ben Skeggs 2022-06-01  256  		*pcctx = cctx;
f48dd293613888 Ben Skeggs 2022-06-01  257  		mutex_unlock(&chan->cgrp->mutex);

This code is correct, but smatch wants people to use "&cgrp->mutex"
constistently instead of "&chan->cgrp->mutex".

f48dd293613888 Ben Skeggs 2022-06-01  258  		return 0;
f48dd293613888 Ben Skeggs 2022-06-01  259  	}
f48dd293613888 Ben Skeggs 2022-06-01  260  
f48dd293613888 Ben Skeggs 2022-06-01  261  	/* Nope - create a fresh one.  But, sub-context first. */
f48dd293613888 Ben Skeggs 2022-06-01  262  	ret = nvkm_cgrp_vctx_get(cgrp, engn, chan, &vctx, client);
f48dd293613888 Ben Skeggs 2022-06-01  263  	if (ret) {
f48dd293613888 Ben Skeggs 2022-06-01  264  		CHAN_ERROR(chan, "vctx %d[%s]: %d", engn->id, engn->engine->subdev.name, ret);
f48dd293613888 Ben Skeggs 2022-06-01  265  		goto done;
f48dd293613888 Ben Skeggs 2022-06-01  266  	}
f48dd293613888 Ben Skeggs 2022-06-01  267  
f48dd293613888 Ben Skeggs 2022-06-01  268  	/* Now, create the channel context - to track engine binding. */
f48dd293613888 Ben Skeggs 2022-06-01  269  	CHAN_TRACE(chan, "ctor cctx %d[%s]", engn->id, engn->engine->subdev.name);
f48dd293613888 Ben Skeggs 2022-06-01  270  	if (!(cctx = *pcctx = kzalloc(sizeof(*cctx), GFP_KERNEL))) {
f48dd293613888 Ben Skeggs 2022-06-01  271  		nvkm_cgrp_vctx_put(cgrp, &vctx);
f48dd293613888 Ben Skeggs 2022-06-01  272  		ret = -ENOMEM;
f48dd293613888 Ben Skeggs 2022-06-01  273  		goto done;
f48dd293613888 Ben Skeggs 2022-06-01  274  	}
f48dd293613888 Ben Skeggs 2022-06-01  275  
f48dd293613888 Ben Skeggs 2022-06-01  276  	cctx->vctx = vctx;
f48dd293613888 Ben Skeggs 2022-06-01  277  	refcount_set(&cctx->refs, 1);
f48dd293613888 Ben Skeggs 2022-06-01  278  	refcount_set(&cctx->uses, 0);
f48dd293613888 Ben Skeggs 2022-06-01  279  	list_add_tail(&cctx->head, &chan->cctxs);
f48dd293613888 Ben Skeggs 2022-06-01  280  done:
f48dd293613888 Ben Skeggs 2022-06-01  281  	mutex_unlock(&cgrp->mutex);
f48dd293613888 Ben Skeggs 2022-06-01 @282  	return ret;
f48dd293613888 Ben Skeggs 2022-06-01  283  }

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