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Stop enforcing additional reference on all cdevs, which was introduced

Browse Source 
in r277199.  Acquire the neccessary reference in delist_dev_locked()
and inform destroy_devl() about it using CDP_UNREF_DTR flag.

Fix some style nits, add asserts.

Discussed with:	hselasky
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2015-01-19 17:36:52 +00:00
parent a57a934a38
commit 3b50dff506
3 changed files with 29 additions and 11 deletions

6
sys/fs/devfs/devfs_devs.c

@ -137,12 +137,6 @@ devfs_alloc(int flags)
vfs_timestamp(&ts);
cdev->si_atime = cdev->si_mtime = cdev->si_ctime = ts;
cdev->si_cred = NULL;
/*
* Avoid race with dev_rel() by setting the initial
* reference count to 1. This last reference is taken
* by the destroy_dev() function.
*/
cdev->si_refcount = 1;
return (cdev);
}

1
sys/fs/devfs/devfs_int.h

@ -56,6 +56,7 @@ struct cdev_priv {
u_int cdp_flags;
#define CDP_ACTIVE (1 << 0)
#define CDP_SCHED_DTR (1 << 1)
#define CDP_UNREF_DTR (1 << 2)
u_int cdp_inuse;
u_int cdp_maxdirent;

33
sys/kern/kern_conf.c

@ -116,6 +116,8 @@ dev_free_devlocked(struct cdev *cdev)
mtx_assert(&devmtx, MA_OWNED);
cdp = cdev2priv(cdev);
KASSERT((cdp->cdp_flags & CDP_UNREF_DTR) == 0,
("destroy_dev() was not called after delist_dev(%p)", cdev));
TAILQ_INSERT_HEAD(&cdevp_free_list, cdp, cdp_list);
}
@ -1035,6 +1037,7 @@ destroy_devl(struct cdev *dev)
{
struct cdevsw *csw;
struct cdev_privdata *p;
struct cdev_priv *cdp;
mtx_assert(&devmtx, MA_OWNED);
KASSERT(dev->si_flags & SI_NAMED,
@ -1043,7 +1046,18 @@ destroy_devl(struct cdev *dev)
("WARNING: Driver mistake: destroy_dev on eternal %d\n",
dev2unit(dev)));
devfs_destroy(dev);
cdp = cdev2priv(dev);
if ((cdp->cdp_flags & CDP_UNREF_DTR) == 0) {
/*
* Avoid race with dev_rel(), e.g. from the populate
* loop. If CDP_UNREF_DTR flag is set, the reference
* to be dropped at the end of destroy_devl() was
* already taken by delist_dev_locked().
*/
dev_refl(dev);
devfs_destroy(dev);
}
/* Remove name marking */
dev->si_flags &= ~SI_NAMED;
@ -1103,19 +1117,27 @@ destroy_devl(struct cdev *dev)
}
}
dev->si_flags &= ~SI_ALIAS;
dev->si_refcount--; /* Avoid race with dev_rel() */
cdp->cdp_flags &= ~CDP_UNREF_DTR;
dev->si_refcount--;
if (dev->si_refcount > 0) {
if (dev->si_refcount > 0)
LIST_INSERT_HEAD(&dead_cdevsw.d_devs, dev, si_list);
} else {
else
dev_free_devlocked(dev);
}
}
static void
delist_dev_locked(struct cdev *dev)
{
struct cdev_priv *cdp;
struct cdev *child;
mtx_assert(&devmtx, MA_OWNED);
cdp = cdev2priv(dev);
if ((cdp->cdp_flags & CDP_UNREF_DTR) != 0)
return;
cdp->cdp_flags |= CDP_UNREF_DTR;
dev_refl(dev);
devfs_destroy(dev);
LIST_FOREACH(child, &dev->si_children, si_siblings)
delist_dev_locked(child);
@ -1124,6 +1146,7 @@ delist_dev_locked(struct cdev *dev)
void
delist_dev(struct cdev *dev)
{
dev_lock();
delist_dev_locked(dev);
dev_unlock();