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): [] kasan_quarantine_put+0xf5/0x210 mm/kasan/quarantine.c:220 > hardirqs last disabled at (916): [] __raw_spin_lock_irq include/linux/spinlock_api_smp.h:117 [inline] > hardirqs last disabled at (916): [] _raw_spin_lock_irq+0x41/0x50 kernel/locking/spinlock.c:170 > softirqs last enabled at (0): [] 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: > > __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 --- Fabio M. De Francesco