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devfs: introduce a per-dev lock to protect ->si_devsw

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This allows bumping threadcount without taking the global devmtx lock.

In particular this eliminates contention on said lock while using bhyve
with multiple vms.

Reviewed by:	kib
Tested by:	markj
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D22548
This commit is contained in:
Mateusz Guzik 2019-11-30 16:46:19 +00:00
parent 0f4b850e85
commit a02cab334c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355228
4 changed files with 20 additions and 6 deletions
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3
sys/fs/devfs/devfs_devs.c
View File

@ -138,6 +138,8 @@ devfs_alloc(int flags)
if (cdp == NULL)
return (NULL);
mtx_init(&cdp->cdp_threadlock, "devthrd", NULL, MTX_DEF);
cdp->cdp_dirents = &cdp->cdp_dirent0;
cdev = &cdp->cdp_c;
@ -180,6 +182,7 @@ devfs_free(struct cdev *cdev)
devfs_free_cdp_inode(cdp->cdp_inode);
if (cdp->cdp_maxdirent > 0)
free(cdp->cdp_dirents, M_DEVFS2);
mtx_destroy(&cdp->cdp_threadlock);
free(cdp, M_CDEVP);
}

2
sys/fs/devfs/devfs_int.h
View File

@ -70,6 +70,8 @@ struct cdev_priv {
void *cdp_dtr_cb_arg;
LIST_HEAD(, cdev_privdata) cdp_fdpriv;
struct mtx cdp_threadlock;
};
#define cdev2priv(c) __containerof(c, struct cdev_priv, cdp_c)

20
sys/kern/kern_conf.c
View File

@ -186,16 +186,16 @@ dev_refthread(struct cdev *dev, int *ref)
*ref = 0;
return (dev->si_devsw);
}
dev_lock();
cdp = cdev2priv(dev);
mtx_lock(&cdp->cdp_threadlock);
csw = dev->si_devsw;
if (csw != NULL) {
cdp = cdev2priv(dev);
if ((cdp->cdp_flags & CDP_SCHED_DTR) == 0)
atomic_add_long(&dev->si_threadcount, 1);
else
csw = NULL;
}
dev_unlock();
mtx_unlock(&cdp->cdp_threadlock);
if (csw != NULL)
*ref = 1;
return (csw);
@ -223,19 +223,21 @@ devvn_refthread(struct vnode *vp, struct cdev **devp, int *ref)
}
csw = NULL;
dev_lock();
VI_LOCK(vp);
dev = vp->v_rdev;
if (dev == NULL) {
dev_unlock();
VI_UNLOCK(vp);
return (NULL);
}
cdp = cdev2priv(dev);
mtx_lock(&cdp->cdp_threadlock);
if ((cdp->cdp_flags & CDP_SCHED_DTR) == 0) {
csw = dev->si_devsw;
if (csw != NULL)
atomic_add_long(&dev->si_threadcount, 1);
}
dev_unlock();
mtx_unlock(&cdp->cdp_threadlock);
VI_UNLOCK(vp);
if (csw != NULL) {
*devp = dev;
*ref = 1;
@ -1136,20 +1138,26 @@ destroy_devl(struct cdev *dev)
dev->si_flags &= ~SI_CLONELIST;
}
mtx_lock(&cdp->cdp_threadlock);
csw = dev->si_devsw;
dev->si_devsw = NULL; /* already NULL for SI_ALIAS */
while (csw != NULL && csw->d_purge != NULL && dev->si_threadcount) {
csw->d_purge(dev);
mtx_unlock(&cdp->cdp_threadlock);
msleep(csw, &devmtx, PRIBIO, "devprg", hz/10);
mtx_lock(&cdp->cdp_threadlock);
if (dev->si_threadcount)
printf("Still %lu threads in %s\n",
dev->si_threadcount, devtoname(dev));
}
while (dev->si_threadcount != 0) {
/* Use unique dummy wait ident */
mtx_unlock(&cdp->cdp_threadlock);
msleep(&csw, &devmtx, PRIBIO, "devdrn", hz / 10);
mtx_lock(&cdp->cdp_threadlock);
}
mtx_unlock(&cdp->cdp_threadlock);
dev_unlock();
if ((cdp->cdp_flags & CDP_UNREF_DTR) == 0) {
/* avoid out of order notify events */

1
sys/kern/subr_witness.c
View File

@ -602,6 +602,7 @@ static struct witness_order_list_entry order_lists[] = {
{ "vm map (system)", &lock_class_mtx_sleep },
{ "vnode interlock", &lock_class_mtx_sleep },
{ "cdev", &lock_class_mtx_sleep },
{ "devthrd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* VM