Hi, On Wed, Nov 04, 2020 at 04:18:08AM -0800, syzbot wrote: > syzbot has bisected this issue to: > > commit e918188611f073063415f40fae568fa4d86d9044 > Author: Boqun Feng <boqun.feng@xxxxxxxxx> > Date: Fri Aug 7 07:42:20 2020 +0000 > > locking: More accurate annotations for read_lock() > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14142732500000 > start commit: 4ef8451b Merge tag 'perf-tools-for-v5.10-2020-11-03' of gi.. > git tree: upstream > final oops: https://syzkaller.appspot.com/x/report.txt?x=16142732500000 > console output: https://syzkaller.appspot.com/x/log.txt?x=12142732500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=61033507391c77ff > dashboard link: https://syzkaller.appspot.com/bug?extid=c5e32344981ad9f33750 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15197862500000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13c59f6c500000 > > Reported-by: syzbot+c5e32344981ad9f33750@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: e918188611f0 ("locking: More accurate annotations for read_lock()") > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection Thanks for reporting this, and this is actually a deadlock potential detected by the newly added recursive read deadlock detection as my analysis: https://lore.kernel.org/lkml/20200910071523.GF7922@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Besides, other reports[1][2] are caused by the same problem. I made a fix for this, please have a try and see if it's get fixed. Regards, Boqun [1]: https://lore.kernel.org/lkml/000000000000d7136005aee14bf9@xxxxxxxxxx [2]: https://lore.kernel.org/lkml/0000000000006e29ed05b3009b04@xxxxxxxxxx ----------------------------------------------------->8 >From 7fbe730fcff2d7909be034cf6dc8bf0604d0bf14 Mon Sep 17 00:00:00 2001 From: Boqun Feng <boqun.feng@xxxxxxxxx> Date: Thu, 5 Nov 2020 14:02:57 +0800 Subject: [PATCH] fs/fcntl: Fix potential deadlock in send_sig{io, urg}() 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@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-by: syzbot+c5e32344981ad9f33750@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> --- fs/fcntl.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 19ac5baad50f..05b36b28f2e8 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -781,9 +781,10 @@ void send_sigio(struct fown_struct *fown, int fd, int band) { 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; @@ -804,7 +805,7 @@ void send_sigio(struct fown_struct *fown, int fd, int band) 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, @@ -819,9 +820,10 @@ 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; @@ -844,7 +846,7 @@ 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; } -- 2.28.0
