From: Linus Torvalds Subject: 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: Linus Torvalds Tested-by: Bruce Fields --- fs/fcntl.c | 62 ++++++++++++++++++++++++++++++++++++++++----------- fs/locks.c | 17 +++++++++++++- include/linux/fs.h | 5 ++++ 3 files changed, 69 insertions(+), 15 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index f8cc34f..ecc8b39 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 +666,31 @@ 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! 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. + */ +void fasync_free(struct fasync_struct *new) +{ + kmem_cache_free(fasync_cache, new); +} + +/* + * Insert a new entry into the fasync list. Return the pointer to the + * old one if we didn't use the new 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 *fasync_insert_entry(int fd, struct file *filp, struct fasync_struct **fapp, struct fasync_struct *new) { - struct fasync_struct *new, *fa, **fp; - int result = 0; - - new = kmem_cache_alloc(fasync_cache, GFP_KERNEL); - if (!new) - return -ENOMEM; + struct fasync_struct *fa, **fp; spin_lock(&filp->f_lock); spin_lock(&fasync_lock); @@ -691,8 +701,6 @@ 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 +710,39 @@ 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. + */ +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);