Commit f7347ce4 authored by Linus Torvalds's avatar Linus Torvalds Committed by Arnd Bergmann
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fasync: re-organize fasync entry insertion to allow it under a spinlock 



You currently cannot use "fasync_helper()" in an atomic environment to
insert a new fasync entry, because it will need to allocate the new
"struct fasync_struct".

Yet fcntl_setlease() wants to call this under lock_flocks(), which is in
the process of being converted from the BKL to a spinlock.

In order to fix this, this abstracts out the actual fasync list
insertion and the fasync allocations into functions of their own, and
teaches fs/locks.c to pre-allocate the fasync_struct entry.  That way
the actual list insertion can happen while holding the required
spinlock.

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
[bfields@redhat.com: rebase on top of my changes to Arnd's patch]
Tested-by: default avatarJ. Bruce Fields <bfields@redhat.com>
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
parent c5b1f0d9

fs/fcntl.c

+50 −16
Original line number Diff line number Diff line
@@ -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;

}



/*

fs/locks.c

+17 −1
Original line number Diff line number Diff line
@@ -1505,6 +1505,7 @@ EXPORT_SYMBOL_GPL(vfs_setlease); 
int fcntl_setlease(unsigned int fd, struct file *filp, long arg)

{

	struct file_lock *fl;

	struct fasync_struct *new;

	struct inode *inode = filp->f_path.dentry->d_inode;

	int error;
@@ -1512,12 +1513,25 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg) 
	if (IS_ERR(fl))

		return PTR_ERR(fl);



	new = fasync_alloc();

	if (!new) {

		locks_free_lock(fl);

		return -ENOMEM;

	}

	lock_flocks();

	error = __vfs_setlease(filp, arg, &fl);

	if (error || arg == F_UNLCK)

		goto out_unlock;



	error = fasync_helper(fd, filp, 1, &fl->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, &fl->fl_fasync, new))

		new = NULL;



	if (error < 0) {

		/* remove lease just inserted by setlease */

		fl->fl_type = F_UNLCK | F_INPROGRESS;
@@ -1529,6 +1543,8 @@ 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;

}

include/linux/fs.h

+5 −0
Original line number Diff line number Diff line
@@ -1302,6 +1302,11 @@ 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);

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