From: Boqun Feng boqun.feng@gmail.com
commit 8d1ddb5e79374fb277985a6b3faa2ed8631c5b4c upstream.
Syzbot reports a potential deadlock found by the newly added recursive read deadlock detection in lockdep:
[...] ======================================================== [...] WARNING: possible irq lock inversion dependency detected [...] 5.9.0-rc2-syzkaller #0 Not tainted [...] -------------------------------------------------------- [...] syz-executor.1/10214 just changed the state of lock: [...] ffff88811f506338 (&f->f_owner.lock){.+..}-{2:2}, at: send_sigurg+0x1d/0x200 [...] but this lock was taken by another, HARDIRQ-safe lock in the past: [...] (&dev->event_lock){-...}-{2:2} [...] [...] [...] and interrupts could create inverse lock ordering between them. [...] [...] [...] other info that might help us debug this: [...] Chain exists of: [...] &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock [...] [...] Possible interrupt unsafe locking scenario: [...] [...] CPU0 CPU1 [...] ---- ---- [...] lock(&f->f_owner.lock); [...] local_irq_disable(); [...] lock(&dev->event_lock); [...] lock(&new->fa_lock); [...] <Interrupt> [...] lock(&dev->event_lock); [...] [...] *** DEADLOCK ***
The corresponding deadlock case is as followed:
CPU 0 CPU 1 CPU 2 read_lock(&fown->lock); spin_lock_irqsave(&dev->event_lock, ...) write_lock_irq(&filp->f_owner.lock); // wait for the lock read_lock(&fown-lock); // have to wait until the writer release // due to the fairness <interrupted> spin_lock_irqsave(&dev->event_lock); // wait for the lock
The lock dependency on CPU 1 happens if there exists a call sequence:
input_inject_event(): spin_lock_irqsave(&dev->event_lock,...); input_handle_event(): input_pass_values(): input_to_handler(): handler->event(): // evdev_event() evdev_pass_values(): spin_lock(&client->buffer_lock); __pass_event(): kill_fasync(): kill_fasync_rcu(): read_lock(&fa->fa_lock); send_sigio(): read_lock(&fown->lock);
To fix this, make the reader in send_sigurg() and send_sigio() use read_lock_irqsave() and read_lock_irqrestore().
Reported-by: syzbot+22e87cdf94021b984aa6@syzkaller.appspotmail.com Reported-by: syzbot+c5e32344981ad9f33750@syzkaller.appspotmail.com Signed-off-by: Boqun Feng boqun.feng@gmail.com Signed-off-by: Jeff Layton jlayton@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/fcntl.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -779,9 +779,10 @@ void send_sigio(struct fown_struct *fown { struct task_struct *p; enum pid_type type; + unsigned long flags; struct pid *pid; - read_lock(&fown->lock); + read_lock_irqsave(&fown->lock, flags);
type = fown->pid_type; pid = fown->pid; @@ -802,7 +803,7 @@ void send_sigio(struct fown_struct *fown read_unlock(&tasklist_lock); } out_unlock_fown: - read_unlock(&fown->lock); + read_unlock_irqrestore(&fown->lock, flags); }
static void send_sigurg_to_task(struct task_struct *p, @@ -817,9 +818,10 @@ int send_sigurg(struct fown_struct *fown struct task_struct *p; enum pid_type type; struct pid *pid; + unsigned long flags; int ret = 0; - read_lock(&fown->lock); + read_lock_irqsave(&fown->lock, flags);
type = fown->pid_type; pid = fown->pid; @@ -842,7 +844,7 @@ int send_sigurg(struct fown_struct *fown read_unlock(&tasklist_lock); } out_unlock_fown: - read_unlock(&fown->lock); + read_unlock_irqrestore(&fown->lock, flags); return ret; }