path: root/fs/fcntl.c
diff options
authorKirill Tkhai <ktkhai@virtuozzo.com>2018-04-05 14:58:06 +0300
committerJeff Layton <jlayton@redhat.com>2018-05-01 07:39:50 -0400
commit7a107c0f55a3b4c6f84a4323df5610360bde1684 (patch)
tree776ce70555dbb4714b1ea10f6f10d06a767f0294 /fs/fcntl.c
parentMerge tag 'errseq-v4.17' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux (diff)
fasync: Fix deadlock between task-context and interrupt-context kill_fasync()
I observed the following deadlock between them: [task 1] [task 2] [task 3] kill_fasync() mm_update_next_owner() copy_process() spin_lock_irqsave(&fa->fa_lock) read_lock(&tasklist_lock) write_lock_irq(&tasklist_lock) send_sigio() <IRQ> ... read_lock(&fown->lock) kill_fasync() ... read_lock(&tasklist_lock) spin_lock_irqsave(&fa->fa_lock) ... Task 1 can't acquire read locked tasklist_lock, since there is already task 3 expressed its wish to take the lock exclusive. Task 2 holds the read locked lock, but it can't take the spin lock. Also, there is possible another deadlock (which I haven't observed): [task 1] [task 2] f_getown() kill_fasync() read_lock(&f_own->lock) spin_lock_irqsave(&fa->fa_lock,) <IRQ> send_sigio() write_lock_irq(&f_own->lock) kill_fasync() read_lock(&fown->lock) spin_lock_irqsave(&fa->fa_lock,) Actually, we do not need exclusive fa->fa_lock in kill_fasync_rcu(), as it guarantees fa->fa_file->f_owner integrity only. It may seem, that it used to give a task a small possibility to receive two sequential signals, if there are two parallel kill_fasync() callers, and task handles the first signal fastly, but the behaviour won't become different, since there is exclusive sighand lock in do_send_sig_info(). The patch converts fa_lock into rwlock_t, and this fixes two above deadlocks, as rwlock is allowed to be taken from interrupt handler by qrwlock design. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> Signed-off-by: Jeff Layton <jlayton@redhat.com>
Diffstat (limited to 'fs/fcntl.c')
1 files changed, 7 insertions, 8 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c
index d737ff082472..c42169459298 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -871,9 +871,9 @@ int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp)
if (fa->fa_file != filp)
- spin_lock_irq(&fa->fa_lock);
+ write_lock_irq(&fa->fa_lock);
fa->fa_file = NULL;
- spin_unlock_irq(&fa->fa_lock);
+ write_unlock_irq(&fa->fa_lock);
*fp = fa->fa_next;
call_rcu(&fa->fa_rcu, fasync_free_rcu);
@@ -918,13 +918,13 @@ struct fasync_struct *fasync_insert_entry(int fd, struct file *filp, struct fasy
if (fa->fa_file != filp)
- spin_lock_irq(&fa->fa_lock);
+ write_lock_irq(&fa->fa_lock);
fa->fa_fd = fd;
- spin_unlock_irq(&fa->fa_lock);
+ write_unlock_irq(&fa->fa_lock);
goto out;
- spin_lock_init(&new->fa_lock);
+ rwlock_init(&new->fa_lock);
new->magic = FASYNC_MAGIC;
new->fa_file = filp;
new->fa_fd = fd;
@@ -987,14 +987,13 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
while (fa) {
struct fown_struct *fown;
- unsigned long flags;
if (fa->magic != FASYNC_MAGIC) {
printk(KERN_ERR "kill_fasync: bad magic number in "
- spin_lock_irqsave(&fa->fa_lock, flags);
+ read_lock(&fa->fa_lock);
if (fa->fa_file) {
fown = &fa->fa_file->f_owner;
/* Don't send SIGURG to processes which have not set a
@@ -1003,7 +1002,7 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band)
if (!(sig == SIGURG && fown->signum == 0))
send_sigio(fown, fa->fa_fd, band);
- spin_unlock_irqrestore(&fa->fa_lock, flags);
+ read_unlock(&fa->fa_lock);
fa = rcu_dereference(fa->fa_next);