efi: Don't use spinlocks for efi vars

All efivars operations are protected by a spinlock which prevents
interruptions and preemption. This is too restricted, we just need a
lock preventing concurrency.
The idea is to use a semaphore of count 1 and to have two ways of
locking, depending on the context:
- In interrupt context, we call down_trylock(), if it fails we return
  an error
- In normal context, we call down_interruptible()

We don't use a mutex here because the mutex_trylock() function must not
be called from interrupt context, whereas the down_trylock() can.

Signed-off-by: Sylvain Chouleur <sylvain.chouleur@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

2 files changed, 11 insertions, 3 deletions

diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index 1d73fc6dba13..cbb50cadcffc 100644
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -105,7 +105,10 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 
 	inode->i_private = var;
 
-	efivar_entry_add(var, &efivarfs_list);
+	err = efivar_entry_add(var, &efivarfs_list);
+	if (err)
+		goto out;
+
 	d_instantiate(dentry, inode);
 	dget(dentry);
 out:
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 688ccc16b702..01e3d6e53944 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -161,7 +161,9 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	kfree(name);
 
 	efivar_entry_size(entry, &size);
-	efivar_entry_add(entry, &efivarfs_list);
+	err = efivar_entry_add(entry, &efivarfs_list);
+	if (err)
+		goto fail_inode;
 
 	inode_lock(inode);
 	inode->i_private = entry;
@@ -182,7 +184,10 @@ fail:
 
 static int efivarfs_destroy(struct efivar_entry *entry, void *data)
 {
-	efivar_entry_remove(entry);
+	int err = efivar_entry_remove(entry);
+
+	if (err)
+		return err;
 	kfree(entry);
 	return 0;
 }