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xen: privcmd: Switch from mutex to spinlock for irqfds

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irqfd_wakeup() gets EPOLLHUP, when it is called by
eventfd_release() by way of wake_up_poll(&ctx->wqh, EPOLLHUP), which
gets called under spin_lock_irqsave(). We can't use a mutex here as it
will lead to a deadlock.

Fix it by switching over to a spin lock.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/a66d7a7a9001424d432f52a9fc3931a1f345464f.1718703669.git.viresh.kumar@linaro.org
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Viresh Kumar 2024-06-18 15:12:28 +05:30 committed by Juergen Gross
parent 7cd23c1817
commit 1c68259309
1 changed files with 15 additions and 10 deletions
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25
drivers/xen/privcmd.c
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@ -846,7 +846,7 @@ out:
#ifdef CONFIG_XEN_PRIVCMD_EVENTFD
/* Irqfd support */
static struct workqueue_struct *irqfd_cleanup_wq;
static DEFINE_MUTEX(irqfds_lock);
static DEFINE_SPINLOCK(irqfds_lock);
static LIST_HEAD(irqfds_list);
struct privcmd_kernel_irqfd {
@ -910,9 +910,11 @@ irqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode, int sync, void *key)
irqfd_inject(kirqfd);
if (flags & EPOLLHUP) {
mutex_lock(&irqfds_lock);
unsigned long flags;
spin_lock_irqsave(&irqfds_lock, flags);
irqfd_deactivate(kirqfd);
mutex_unlock(&irqfds_lock);
spin_unlock_irqrestore(&irqfds_lock, flags);
}
return 0;
@ -930,6 +932,7 @@ irqfd_poll_func(struct file *file, wait_queue_head_t *wqh, poll_table *pt)
static int privcmd_irqfd_assign(struct privcmd_irqfd *irqfd)
{
struct privcmd_kernel_irqfd *kirqfd, *tmp;
unsigned long flags;
__poll_t events;
struct fd f;
void *dm_op;
@ -969,18 +972,18 @@ static int privcmd_irqfd_assign(struct privcmd_irqfd *irqfd)
init_waitqueue_func_entry(&kirqfd->wait, irqfd_wakeup);
init_poll_funcptr(&kirqfd->pt, irqfd_poll_func);
mutex_lock(&irqfds_lock);
spin_lock_irqsave(&irqfds_lock, flags);
list_for_each_entry(tmp, &irqfds_list, list) {
if (kirqfd->eventfd == tmp->eventfd) {
ret = -EBUSY;
mutex_unlock(&irqfds_lock);
spin_unlock_irqrestore(&irqfds_lock, flags);
goto error_eventfd;
}
}
list_add_tail(&kirqfd->list, &irqfds_list);
mutex_unlock(&irqfds_lock);
spin_unlock_irqrestore(&irqfds_lock, flags);
/*
* Check if there was an event already pending on the eventfd before we
@ -1012,12 +1015,13 @@ static int privcmd_irqfd_deassign(struct privcmd_irqfd *irqfd)
{
struct privcmd_kernel_irqfd *kirqfd;
struct eventfd_ctx *eventfd;
unsigned long flags;
eventfd = eventfd_ctx_fdget(irqfd->fd);
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
mutex_lock(&irqfds_lock);
spin_lock_irqsave(&irqfds_lock, flags);
list_for_each_entry(kirqfd, &irqfds_list, list) {
if (kirqfd->eventfd == eventfd) {
@ -1026,7 +1030,7 @@ static int privcmd_irqfd_deassign(struct privcmd_irqfd *irqfd)
}
}
mutex_unlock(&irqfds_lock);
spin_unlock_irqrestore(&irqfds_lock, flags);
eventfd_ctx_put(eventfd);
@ -1074,13 +1078,14 @@ static int privcmd_irqfd_init(void)
static void privcmd_irqfd_exit(void)
{
struct privcmd_kernel_irqfd *kirqfd, *tmp;
unsigned long flags;
mutex_lock(&irqfds_lock);
spin_lock_irqsave(&irqfds_lock, flags);
list_for_each_entry_safe(kirqfd, tmp, &irqfds_list, list)
irqfd_deactivate(kirqfd);
mutex_unlock(&irqfds_lock);
spin_unlock_irqrestore(&irqfds_lock, flags);
destroy_workqueue(irqfd_cleanup_wq);
}