From: Roger Pau Monne roger.pau@citrix.com
[ Upstream commit c0dccad87cf68fc6012aec7567e354353097ec1a ]
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: 02e19f9c7cac ('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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/hvc/hvc_xen.c | 46 ++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 17 deletions(-)
diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c index 7948660e042f..6f387a4fd96a 100644 --- a/drivers/tty/hvc/hvc_xen.c +++ b/drivers/tty/hvc/hvc_xen.c @@ -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;
@@ -583,10 +593,12 @@ 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);