LinuxKPI: Implement get_file_rcu()

get_file_rcu() grabs a file if the file->f_count is not zero.

Required by drm-kmod 5.6

Reviewed by:	hselasky, manu (previous version)
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D31672

2 files changed, 12 insertions, 1 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/fs.h b/sys/compat/linuxkpi/common/include/linux/fs.h
index 38911c276216..eaf806b6732c 100644
--- a/sys/compat/linuxkpi/common/include/linux/fs.h
+++ b/sys/compat/linuxkpi/common/include/linux/fs.h
@@ -108,6 +108,8 @@ struct linux_file {
 
 	/* pointer to associated character device, if any */
 	struct linux_cdev *f_cdev;
+
+	struct rcu_head	rcu;
 };
 
 #define	file		linux_file
@@ -254,6 +256,13 @@ get_file(struct linux_file *f)
 	return (f);
 }
 
+static inline bool
+get_file_rcu(struct linux_file *f)
+{
+	return (refcount_acquire_if_not_zero(
+	    f->_file == NULL ? &f->f_count : &f->_file->f_count));
+}
+
 static inline struct inode *
 igrab(struct inode *inode)
 {
diff --git a/sys/compat/linuxkpi/common/src/linux_compat.c b/sys/compat/linuxkpi/common/src/linux_compat.c
index 7ea33c9a0d8d..f15b9396525c 100644
--- a/sys/compat/linuxkpi/common/src/linux_compat.c
+++ b/sys/compat/linuxkpi/common/src/linux_compat.c
@@ -90,6 +90,7 @@ __FBSDID("$FreeBSD$");
 #include <linux/poll.h>
 #include <linux/smp.h>
 #include <linux/wait_bit.h>
+#include <linux/rcupdate.h>
 
 #if defined(__i386__) || defined(__amd64__)
 #include <asm/smp.h>
@@ -472,7 +473,7 @@ linux_file_free(struct linux_file *filp)
 	if (filp->_file == NULL) {
 		if (filp->f_shmem != NULL)
 			vm_object_deallocate(filp->f_shmem);
-		kfree(filp);
+		kfree_rcu(filp, rcu);
 	} else {
 		/*
 		 * The close method of the character device or file
@@ -1538,6 +1539,7 @@ linux_file_close(struct file *file, struct thread *td)
 	ldev = filp->f_cdev;
 	if (ldev != NULL)
 		linux_cdev_deref(ldev);
+	linux_synchronize_rcu(RCU_TYPE_REGULAR);
 	kfree(filp);
 
 	return (error);