Re: nfsd changes for 2.6.37

Linus Torvalds
2010-10-27T16:13:10Z

[-- Attachment #1: Type: text/plain, Size: 870 bytes --]

On Wed, Oct 27, 2010 at 8:23 AM, Arnd Bergmann <arnd@arndb.de> wrote:
>
> locks_delete_lock is also called with lock_flocks held and calls
> fasync_helper...

We don't really have to use fasync_helper.

In fact, the whole interface is pretty broken for something like file
locking, which isn't actually "fasync()". That whole "on/off as an
argument" is just crazy. It would be _trivial_ to expose a version of
fasync_helper() that takes a pre-allocated fasync_struct for add, and
that has separate helper functions for the add/delete case so that you
don't have the pointless crazy arguments (for "delete" the "fd"
argument is useless, and I do hate "modal" functions that take what
they should do as a flag).

Then fcntl_setlease() would trivially just allocate the dang thing before.

Something like the attached (UNTESTED!) perhaps?

Linus

[-- Attachment #2: patch.diff --]
[-- Type: text/x-patch, Size: 5305 bytes --]

fs/fcntl.c | 66 +++++++++++++++++++++++++++++++++++++++------------
fs/locks.c | 17 ++++++++++++-
include/linux/fs.h | 5 ++++
3 files changed, 71 insertions(+), 17 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index f8cc34f..dcdbc6f 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -640,7 +640,7 @@ static void fasync_free_rcu(struct rcu_head *head)
* match the state "is the filp on a fasync list".
*
*/
-static int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
+int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
{
struct fasync_struct *fa, **fp;
int result = 0;
@@ -666,21 +666,28 @@ static int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
return result;
}

+struct fasync_struct *fasync_alloc(void)
+{
+ return kmem_cache_alloc(fasync_cache, GFP_KERNEL);
+}
+
/*
- * Add a fasync entry. Return negative on error, positive if
- * added, and zero if did nothing but change an existing one.
- *
- * NOTE! It is very important that the FASYNC flag always
- * match the state "is the filp on a fasync list".
+ * NOTE! This can be used only for unused fasync entries:
+ * entries that actually got inserted on the fasync list
+ * need to be released by rcu - see fasync_remove_entry.
*/
-static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fapp)
+void fasync_free(struct fasync_struct *new)
{
- struct fasync_struct *new, *fa, **fp;
- int result = 0;
+ kmem_cache_free(fasync_cache, new);
+}

- new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
- if (!new)
- return -ENOMEM;
+/*
+ * Insert a new entry into the fasync list. Return the pointer to the
+ * old one if we didn't use the new one.
+ */
+struct fasync_struct *fasync_insert_entry(int fd, struct file *filp, struct fasync_struct **fapp, struct fasync_struct *new)
+{
+ struct fasync_struct *fa, **fp;

spin_lock(&filp->f_lock);
spin_lock(&fasync_lock);
@@ -691,8 +698,6 @@ static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fa
spin_lock_irq(&fa->fa_lock);
fa->fa_fd = fd;
spin_unlock_irq(&fa->fa_lock);
-
- kmem_cache_free(fasync_cache, new);
goto out;
}

@@ -702,13 +707,42 @@ static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fa
new->fa_fd = fd;
new->fa_next = *fapp;
rcu_assign_pointer(*fapp, new);
- result = 1;
filp->f_flags |= FASYNC;

out:
spin_unlock(&fasync_lock);
spin_unlock(&filp->f_lock);
- return result;
+ return fa;
+}
+
+/*
+ * Add a fasync entry. Return negative on error, positive if
+ * added, and zero if did nothing but change an existing one.
+ *
+ * NOTE! It is very important that the FASYNC flag always
+ * match the state "is the filp on a fasync list".
+ */
+static int fasync_add_entry(int fd, struct file *filp, struct fasync_struct **fapp)
+{
+ struct fasync_struct *new;
+
+ new = fasync_alloc();
+ if (!new)
+ return -ENOMEM;
+
+ /*
+ * fasync_insert_entry() returns the old (update) entry if
+ * it existed.
+ *
+ * So free the (unused) new entry and return 0 to let the
+ * caller know that we didn't add any new fasync entries.
+ */
+ if (fasync_insert_entry(fd, filp, fapp, new)) {
+ fasync_free(new);
+ return 0;
+ }
+
+ return 1;
}

/*
diff --git a/fs/locks.c b/fs/locks.c
index 4de3a26..9ff3f66 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1515,6 +1515,7 @@ EXPORT_SYMBOL_GPL(vfs_setlease);
int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
{
struct file_lock fl, *flp = &fl;
+ struct fasync_struct *new;
struct inode *inode = filp->f_path.dentry->d_inode;
int error;

@@ -1523,13 +1524,25 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
if (error)
return error;

+ new = fasync_alloc();
+ if (!new)
+ return -ENOMEM;
+
lock_flocks();

error = __vfs_setlease(filp, arg, &flp);
if (error || arg == F_UNLCK)
goto out_unlock;

- error = fasync_helper(fd, filp, 1, &flp->fl_fasync);
+ /*
+ * fasync_insert_entry() returns the old entry if any.
+ * If there was no old entry, then it used 'new' and
+ * inserted it into the fasync list. Clear new so that
+ * we don't release it here.
+ */
+ if (!fasync_insert_entry(fd, filp, &flp->fl_fasync, new))
+ new = NULL;
+
if (error < 0) {
/* remove lease just inserted by setlease */
flp->fl_type = F_UNLCK | F_INPROGRESS;
@@ -1541,6 +1554,8 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
out_unlock:
unlock_flocks();
+ if (new)
+ fasync_free(new);
return error;
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 240eb1d..d487772 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1310,6 +1310,11 @@ struct fasync_struct {

/* SMP safe fasync helpers: */
extern int fasync_helper(int, struct file *, int, struct fasync_struct **);
+extern struct fasync_struct *fasync_insert_entry(int, struct file *, struct fasync_struct **, struct fasync_struct *);
+extern int fasync_remove_entry(struct file *, struct fasync_struct **);
+extern struct fasync_struct *fasync_alloc(void);
+extern void fasync_free(struct fasync_struct *);
+
/* can be called from interrupts */
extern void kill_fasync(struct fasync_struct **, int, int);