Messages in this thread Patch in this message | | | From | "Fabio M. De Francesco" <> | Subject | Re: [syzbot] BUG: sleeping function called from invalid context in __might_resched | Date | Tue, 16 Nov 2021 10:13:19 +0100 |
| |
On Tuesday, November 16, 2021 9:53:53 AM CET Fabio M. De Francesco wrote: > On Tuesday, November 16, 2021 9:09:11 AM CET syzbot wrote: > > Hello, > > > > syzbot has tested the proposed patch but the reproducer is still triggering > an issue: > > BUG: sleeping function called from invalid context in __might_resched > > > > BUG: sleeping function called from invalid context at kernel/printk/ > printk.c:2522 > > in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 8755, name: syz- > executor.2 > > preempt_count: 1, expected: 0 > > RCU nest depth: 0, expected: 0 > > 3 locks held by syz-executor.2/8755: > > #0: ffff888070c9a098 > > (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/ > tty/tty_ldisc.c:252 > > #1: ffff888070c9a468 > > (&tty->flow.lock){....}-{2:2}, at: spin_lock_irq include/linux/ spinlock.h: > 374 [inline] > > (&tty->flow.lock){....}-{2:2}, at: n_tty_ioctl_helper+0xb6/0x2d0 drivers/ > tty/tty_ioctl.c:877 > > #2: ffff888070c9a098 (&tty->ldisc_sem){++++}-{0:0}, at: > tty_ldisc_ref+0x1d/0x80 drivers/tty/tty_ldisc.c:273 > > irq event stamp: 916 > > hardirqs last enabled at (915): [<ffffffff81beabd5>] > kasan_quarantine_put+0xf5/0x210 mm/kasan/quarantine.c:220 > > hardirqs last disabled at (916): [<ffffffff8950a731>] __raw_spin_lock_irq > include/linux/spinlock_api_smp.h:117 [inline] > > hardirqs last disabled at (916): [<ffffffff8950a731>] > _raw_spin_lock_irq+0x41/0x50 kernel/locking/spinlock.c:170 > > softirqs last enabled at (0): [<ffffffff8144cf0c>] copy_process+0x1e8c/ > 0x75a0 kernel/fork.c:2136 > > softirqs last disabled at (0): [<0000000000000000>] 0x0 > > Preemption disabled at: > > [<0000000000000000>] 0x0 > > CPU: 1 PID: 8755 Comm: syz-executor.2 Not tainted 5.16.0-rc1-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > > Call Trace: > > <TASK> > > __dump_stack lib/dump_stack.c:88 [inline] > > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > > __might_resched.cold+0x222/0x26b kernel/sched/core.c:9542 > > console_lock+0x17/0x80 kernel/printk/printk.c:2522 > > con_flush_chars drivers/tty/vt/vt.c:3365 [inline] > > con_flush_chars+0x35/0x90 drivers/tty/vt/vt.c:3357 > > con_write+0x2c/0x40 drivers/tty/vt/vt.c:3296 > > The reproducer is still triggering an issue, but this time it looks like it > is triggered by a different path of execution. > > The same invalid "in_interrupt()" test is also in con_flush_chars(). > > Let's try to remove it too... > > My first idea would be to replace "if (in_interrupt())" with the same > "preempt_count() || irqs_disabled()" I used in do_con_write(). However I > noticed that both do_con_write() and con_flush_chars() are only called from > inside con_write() (which, aside from calling those functions, does nothing > else). > > So why not remove the if (in_interrupt()) from both them and use if > (preempt_count() || irqs_disabled()) just once in con_write()? > > I think this should be the right solution, but I prefer to go one step at a > time. > > Therefore, I'll (1) use the same (redundant, if it was used in con_write()) > test also in con_flush_chars(), (2) wait for Syzbot to confirm that it fixes > the bug, and (3) wait for maintainers review and suggestions about whether or > not moving those tests one level upper. >
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > --- > Fabio M. De Francesco >
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 7359c3e80d63..46511d1ac6ee 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -2902,7 +2902,7 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co struct vt_notifier_param param; bool rescan; - if (in_interrupt()) + if (preempt_count() || irqs_disabled()) return count; console_lock(); @@ -3358,7 +3358,7 @@ static void con_flush_chars(struct tty_struct *tty) { struct vc_data *vc; - if (in_interrupt()) /* from flush_to_ldisc */ + if (preempt_count() || irqs_disabled()) /* from flush_to_ldisc */ return; /* if we race with con_close(), vt may be null */ | |