On 2020-04-16, John Ogness <john.ogness@xxxxxxxxxxxxx> wrote: >> - Is there a scenario in fbcon where this function is invoked and >> console_may_schedule is not 0? Sorry, I overlooked that you were specifically asking about fbcon. In console_conditional_schedule() when it is going to call cond_resched(), I added a WARN_ON() with a condition that it would only trigger in fbcon. This allowed me to quickly generate a backtrace. This is what showed up (upon hitting the return key in the graphical console): [ 19.694698][ T1301] Call Trace: [ 19.694743][ T1301] dump_stack+0xa0/0xea [ 19.694766][ T1301] console_conditional_schedule+0xac/0xc0 [ 19.694779][ T1301] fbcon_redraw.isra.16+0x1d2/0x460 [ 19.694825][ T1301] fbcon_scroll+0x1b28/0x36d0 [ 19.694872][ T1301] con_scroll+0x2dd/0x650 [ 19.694914][ T1301] lf+0x240/0x2a0 [ 19.694930][ T1301] ? con_scroll+0x650/0x650 [ 19.694948][ T1301] ? find_held_lock+0x36/0x1d0 [ 19.694983][ T1301] do_con_trol+0x33c/0x6720 [ 19.695001][ T1301] ? lock_downgrade+0x850/0x850 [ 19.695019][ T1301] ? reset_palette+0x210/0x210 [ 19.695051][ T1301] ? __kasan_check_read+0x11/0x20 [ 19.695080][ T1301] ? __atomic_notifier_call_chain+0x9a/0x110 [ 19.695108][ T1301] do_con_write.part.28+0xae2/0x1ba0 [ 19.695179][ T1301] ? do_con_trol+0x6720/0x6720 [ 19.695195][ T1301] ? mutex_lock_io_nested+0x1240/0x1240 [ 19.695212][ T1301] ? console_unlock+0x67d/0xac0 [ 19.695238][ T1301] ? __kasan_check_write+0x14/0x20 [ 19.695249][ T1301] ? __mutex_unlock_slowpath+0xe5/0x6a0 [ 19.695287][ T1301] con_write+0x24/0x90 [ 19.695305][ T1301] do_output_char+0x4f8/0x710 [ 19.695330][ T1301] n_tty_write+0x52b/0xfc0 [ 19.695345][ T1301] ? __might_fault+0xcb/0x1b0 [ 19.695400][ T1301] ? n_tty_read+0x1900/0x1900 [ 19.695419][ T1301] ? prepare_to_wait_exclusive+0x2f0/0x2f0 [ 19.695444][ T1301] ? __kasan_check_write+0x14/0x20 [ 19.695469][ T1301] tty_write+0x3ba/0x800 [ 19.695492][ T1301] ? n_tty_read+0x1900/0x1900 [ 19.695519][ T1301] __vfs_write+0x66/0x120 [ 19.695541][ T1301] vfs_write+0x19c/0x4b0 [ 19.695568][ T1301] ksys_write+0x110/0x230 [ 19.695588][ T1301] ? __ia32_sys_read+0xb0/0xb0 [ 19.695604][ T1301] ? do_syscall_64+0x1d/0x470 [ 19.695617][ T1301] ? entry_SYSCALL_64_after_hwframe+0x49/0xb3 [ 19.695646][ T1301] __x64_sys_write+0x73/0xb0 [ 19.695664][ T1301] do_syscall_64+0x9a/0x470 [ 19.695684][ T1301] entry_SYSCALL_64_after_hwframe+0x49/0xb3 So the answer to your question is "yes". It would probably be a good idea if vt_console_print() could set console_may_schedule=0 after taking the printing_lock (spinlock). There are probably more of these quirky cases hiding in the kernel. I've taken note of this and will look into it when I get some free cycles. John Ogness
