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Push Giant down one layer

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The /dev/pci device doesn't need GIANT, per se. However, one routine
that it calls, pci_find_dbsf implicitly does. It walks a list that can
change when PCI scans a new bus. With hotplug, this means we could
have a race with that scanning. To prevent that, take out Giant around
scanning the list.

However, given that we have places in the tree that drop giant, if
held when we call into them, the whole use of Giant to protect newbus
may be less effective that we desire, so add a comment about why we're
talking it out, and we'll address the issue when we lock newbus with
something other than Giant.
This commit is contained in:
Warner Losh 2019-11-23 23:43:52 +00:00
parent 0ee420b608
commit dd615d09c4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355037
2 changed files with 7 additions and 4 deletions
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9
sys/dev/pci/pci.c
View File

@ -445,18 +445,21 @@ pci_find_bsf(uint8_t bus, uint8_t slot, uint8_t func)
device_t
pci_find_dbsf(uint32_t domain, uint8_t bus, uint8_t slot, uint8_t func)
{
struct pci_devinfo *dinfo;
struct pci_devinfo *dinfo = NULL;
/* Giant because newbus is Giant locked revisit with newbus locking */
mtx_lock(&Giant);
STAILQ_FOREACH(dinfo, &pci_devq, pci_links) {
if ((dinfo->cfg.domain == domain) &&
(dinfo->cfg.bus == bus) &&
(dinfo->cfg.slot == slot) &&
(dinfo->cfg.func == func)) {
return (dinfo->cfg.dev);
break;
}
}
mtx_unlock(&Giant);
return (NULL);
return (dinfo != NULL ? dinfo->cfg.dev : NULL);
}
/* Find a device_t by vendor/device ID */

2
sys/dev/pci/pci_user.c
View File

@ -119,7 +119,7 @@ static d_ioctl_t pci_ioctl;
struct cdevsw pcicdev = {
.d_version = D_VERSION,
.d_flags = D_NEEDGIANT,
.d_flags = 0,
.d_open = pci_open,
.d_close = pci_close,
.d_ioctl = pci_ioctl,