[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [XEN][PATCH v7 14/19] common/device_tree: Add rwlock for dt_host
Hi Vikram, On 02/06/2023 02:48, Vikram Garhwal wrote: > Dynamic programming ops will modify the dt_host and there might be other > function which are browsing the dt_host at the same time. To avoid the race > conditions, adding rwlock for browsing the dt_host during runtime. > > Reason behind adding rwlock instead of spinlock: > For now, dynamic programming is the sole modifier of dt_host in Xen during > run time. All other access functions like iommu_release_dt_device() > are > just reading the dt_host during run-time. So, there is a need to > protect > others from browsing the dt_host while dynamic programming is > modifying > it. rwlock is better suitable for this task as spinlock won't be able > to > differentiate between read and write access. > > Signed-off-by: Vikram Garhwal <vikram.garhwal@xxxxxxx> > > --- > Changes from v6: > Remove redundant "read_unlock(&dt_host->lock);" in the following case: > XEN_DOMCTL_deassign_device > --- > xen/common/device_tree.c | 4 ++++ > xen/drivers/passthrough/device_tree.c | 15 +++++++++++++++ > xen/include/xen/device_tree.h | 6 ++++++ > 3 files changed, 25 insertions(+) > > diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c > index c5250a1644..c8fcdf8fa1 100644 > --- a/xen/common/device_tree.c > +++ b/xen/common/device_tree.c > @@ -2146,7 +2146,11 @@ int unflatten_device_tree(const void *fdt, struct > dt_device_node **mynodes) > > dt_dprintk(" <- unflatten_device_tree()\n"); > > + /* Init r/w lock for host device tree. */ > + rwlock_init(&dt_host->lock); unflatten_device_tree() is called for dt_host and will also be used when adding a new dt overlay meaning that rwlock_init for dt_host will be called multiple times (even if mynodes != &dt_host) which is rather strange. > + > return 0; > + > } > > static void dt_alias_add(struct dt_alias_prop *ap, > diff --git a/xen/drivers/passthrough/device_tree.c > b/xen/drivers/passthrough/device_tree.c > index 301a5bcd97..f4d9deb624 100644 > --- a/xen/drivers/passthrough/device_tree.c > +++ b/xen/drivers/passthrough/device_tree.c > @@ -112,6 +112,8 @@ int iommu_release_dt_devices(struct domain *d) > if ( !is_iommu_enabled(d) ) > return 0; > > + read_lock(&dt_host->lock); > + > list_for_each_entry_safe(dev, _dev, &hd->dt_devices, domain_list) > { > rc = iommu_deassign_dt_device(d, dev); > @@ -119,10 +121,14 @@ int iommu_release_dt_devices(struct domain *d) > { > dprintk(XENLOG_ERR, "Failed to deassign %s in domain %u\n", > dt_node_full_name(dev), d->domain_id); > + > + read_unlock(&dt_host->lock); > return rc; > } > } > > + read_unlock(&dt_host->lock); > + > return 0; > } > > @@ -246,6 +252,8 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct > domain *d, > int ret; > struct dt_device_node *dev; > > + read_lock(&dt_host->lock); > + > switch ( domctl->cmd ) > { > case XEN_DOMCTL_assign_device: > @@ -295,7 +303,10 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct > domain *d, > spin_unlock(&dtdevs_lock); > > if ( d == dom_io ) > + { > + read_unlock(&dt_host->lock); > return -EINVAL; > + } > > ret = iommu_add_dt_device(dev); > if ( ret < 0 ) > @@ -333,7 +344,10 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct > domain *d, > break; > > if ( d == dom_io ) > + { > + read_unlock(&dt_host->lock); > return -EINVAL; > + } > > ret = iommu_deassign_dt_device(d, dev); > > @@ -348,5 +362,6 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct > domain *d, > break; > } > > + read_unlock(&dt_host->lock); > return ret; > } > diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h > index e239f7de26..dee40d2ea3 100644 > --- a/xen/include/xen/device_tree.h > +++ b/xen/include/xen/device_tree.h > @@ -18,6 +18,7 @@ > #include <xen/string.h> > #include <xen/types.h> > #include <xen/list.h> > +#include <xen/rwlock.h> Sort alphabetically (despite list.h not being placed correctly) > > #define DEVICE_TREE_MAX_DEPTH 16 > > @@ -106,6 +107,11 @@ struct dt_device_node { > struct list_head domain_list; > > struct device dev; > + > + /* > + * Lock that protects r/w updates to unflattened device tree i.e. > dt_host. > + */ No need for multiline comment style > + rwlock_t lock; > }; > > #define dt_to_dev(dt_node) (&(dt_node)->dev) ~Michal
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