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hvc/xen: lock console list traversal 

The currently lockless access to the xen console list in
vtermno_to_xencons() is incorrect, as additions and removals from the
list can happen anytime, and as such the traversal of the list to get
the private console data for a given termno needs to happen with the
lock held.  Note users that modify the list already do so with the
lock taken.

Adjust current lock takers to use the _irq{save,restore} helpers,
since the context in which vtermno_to_xencons() is called can have
interrupts disabled.  Use the _irq{save,restore} set of helpers to
switch the current callers to disable interrupts in the locked region.
I haven't checked if existing users could instead use the _irq
variant, as I think it's safer to use _irq{save,restore} upfront.

While there switch from using list_for_each_entry_safe to
list_for_each_entry: the current entry cursor won't be removed as
part of the code in the loop body, so using the _safe variant is
pointless.

Fixes: 02e19f9c7c ('hvc_xen: implement multiconsole support')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/20221130163611.14686-1-roger.pau@citrix.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Roger Pau Monne 2022-11-30 17:36:02 +01:00 committed by Juergen Gross
parent 37c1785609
commit c0dccad87c
1 changed files with 29 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
drivers/tty/hvc/hvc_xen.c
View File

@ -52,17 +52,22 @@ static DEFINE_SPINLOCK(xencons_lock);
static struct xencons_info *vtermno_to_xencons(int vtermno)
{
struct xencons_info *entry, *n, *ret = NULL;
struct xencons_info *entry, *ret = NULL;
unsigned long flags;
if (list_empty(&xenconsoles))
return NULL;
spin_lock_irqsave(&xencons_lock, flags);
if (list_empty(&xenconsoles)) {
spin_unlock_irqrestore(&xencons_lock, flags);
return NULL;
}
list_for_each_entry_safe(entry, n, &xenconsoles, list) {
list_for_each_entry(entry, &xenconsoles, list) {
if (entry->vtermno == vtermno) {
ret = entry;
break;
}
}
spin_unlock_irqrestore(&xencons_lock, flags);
return ret;
}
@ -223,7 +228,7 @@ static int xen_hvm_console_init(void)
{
int r;
uint64_t v = 0;
unsigned long gfn;
unsigned long gfn, flags;
struct xencons_info *info;
if (!xen_hvm_domain())
@ -258,9 +263,9 @@ static int xen_hvm_console_init(void)
goto err;
info->vtermno = HVC_COOKIE;
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
list_add_tail(&info->list, &xenconsoles);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
return 0;
err:
@ -283,6 +288,7 @@ static int xencons_info_pv_init(struct xencons_info *info, int vtermno)
static int xen_pv_console_init(void)
{
struct xencons_info *info;
unsigned long flags;
if (!xen_pv_domain())
return -ENODEV;
@ -299,9 +305,9 @@ static int xen_pv_console_init(void)
/* already configured */
return 0;
}
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
xencons_info_pv_init(info, HVC_COOKIE);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
return 0;
}
@ -309,6 +315,7 @@ static int xen_pv_console_init(void)
static int xen_initial_domain_console_init(void)
{
struct xencons_info *info;
unsigned long flags;
if (!xen_initial_domain())
return -ENODEV;
@ -323,9 +330,9 @@ static int xen_initial_domain_console_init(void)
info->irq = bind_virq_to_irq(VIRQ_CONSOLE, 0, false);
info->vtermno = HVC_COOKIE;
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
list_add_tail(&info->list, &xenconsoles);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
return 0;
}
@ -380,10 +387,12 @@ static void xencons_free(struct xencons_info *info)
static int xen_console_remove(struct xencons_info *info)
{
unsigned long flags;
xencons_disconnect_backend(info);
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
list_del(&info->list);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
if (info->xbdev != NULL)
xencons_free(info);
else {
@ -464,6 +473,7 @@ static int xencons_probe(struct xenbus_device *dev,
{
int ret, devid;
struct xencons_info *info;
unsigned long flags;
devid = dev->nodename[strlen(dev->nodename) - 1] - '0';
if (devid == 0)
@ -482,9 +492,9 @@ static int xencons_probe(struct xenbus_device *dev,
ret = xencons_connect_backend(dev, info);
if (ret < 0)
goto error;
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
list_add_tail(&info->list, &xenconsoles);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
return 0;
@ -584,10 +594,12 @@ static int __init xen_hvc_init(void)
info->hvc = hvc_alloc(HVC_COOKIE, info->irq, ops, 256);
if (IS_ERR(info->hvc)) {
unsigned long flags;
r = PTR_ERR(info->hvc);
spin_lock(&xencons_lock);
spin_lock_irqsave(&xencons_lock, flags);
list_del(&info->list);
spin_unlock(&xencons_lock);
spin_unlock_irqrestore(&xencons_lock, flags);
if (info->irq)
unbind_from_irqhandler(info->irq, NULL);
kfree(info);