| From 8de3efc8b2bd15af9e7b3819de1e5fb1faf110f4 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Thu, 12 May 2022 20:38:37 -0700 |
| Subject: tty: fix deadlock caused by calling printk() under tty_port->lock |
| |
| From: Qi Zheng <zhengqi.arch@bytedance.com> |
| |
| [ Upstream commit 6b9dbedbe3499fef862c4dff5217cf91f34e43b3 ] |
| |
| pty_write() invokes kmalloc() which may invoke a normal printk() to print |
| failure message. This can cause a deadlock in the scenario reported by |
| syz-bot below: |
| |
| CPU0 CPU1 CPU2 |
| ---- ---- ---- |
| lock(console_owner); |
| lock(&port_lock_key); |
| lock(&port->lock); |
| lock(&port_lock_key); |
| lock(&port->lock); |
| lock(console_owner); |
| |
| As commit dbdda842fe96 ("printk: Add console owner and waiter logic to |
| load balance console writes") said, such deadlock can be prevented by |
| using printk_deferred() in kmalloc() (which is invoked in the section |
| guarded by the port->lock). But there are too many printk() on the |
| kmalloc() path, and kmalloc() can be called from anywhere, so changing |
| printk() to printk_deferred() is too complicated and inelegant. |
| |
| Therefore, this patch chooses to specify __GFP_NOWARN to kmalloc(), so |
| that printk() will not be called, and this deadlock problem can be |
| avoided. |
| |
| Syzbot reported the following lockdep error: |
| |
| ====================================================== |
| WARNING: possible circular locking dependency detected |
| 5.4.143-00237-g08ccc19a-dirty #10 Not tainted |
| ------------------------------------------------------ |
| syz-executor.4/29420 is trying to acquire lock: |
| ffffffff8aedb2a0 (console_owner){....}-{0:0}, at: console_trylock_spinning kernel/printk/printk.c:1752 [inline] |
| ffffffff8aedb2a0 (console_owner){....}-{0:0}, at: vprintk_emit+0x2ca/0x470 kernel/printk/printk.c:2023 |
| |
| but task is already holding lock: |
| ffff8880119c9158 (&port->lock){-.-.}-{2:2}, at: pty_write+0xf4/0x1f0 drivers/tty/pty.c:120 |
| |
| which lock already depends on the new lock. |
| |
| the existing dependency chain (in reverse order) is: |
| |
| -> #2 (&port->lock){-.-.}-{2:2}: |
| __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] |
| _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159 |
| tty_port_tty_get drivers/tty/tty_port.c:288 [inline] <-- lock(&port->lock); |
| tty_port_default_wakeup+0x1d/0xb0 drivers/tty/tty_port.c:47 |
| serial8250_tx_chars+0x530/0xa80 drivers/tty/serial/8250/8250_port.c:1767 |
| serial8250_handle_irq.part.0+0x31f/0x3d0 drivers/tty/serial/8250/8250_port.c:1854 |
| serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1827 [inline] <-- lock(&port_lock_key); |
| serial8250_default_handle_irq+0xb2/0x220 drivers/tty/serial/8250/8250_port.c:1870 |
| serial8250_interrupt+0xfd/0x200 drivers/tty/serial/8250/8250_core.c:126 |
| __handle_irq_event_percpu+0x109/0xa50 kernel/irq/handle.c:156 |
| [...] |
| |
| -> #1 (&port_lock_key){-.-.}-{2:2}: |
| __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] |
| _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159 |
| serial8250_console_write+0x184/0xa40 drivers/tty/serial/8250/8250_port.c:3198 |
| <-- lock(&port_lock_key); |
| call_console_drivers kernel/printk/printk.c:1819 [inline] |
| console_unlock+0x8cb/0xd00 kernel/printk/printk.c:2504 |
| vprintk_emit+0x1b5/0x470 kernel/printk/printk.c:2024 <-- lock(console_owner); |
| vprintk_func+0x8d/0x250 kernel/printk/printk_safe.c:394 |
| printk+0xba/0xed kernel/printk/printk.c:2084 |
| register_console+0x8b3/0xc10 kernel/printk/printk.c:2829 |
| univ8250_console_init+0x3a/0x46 drivers/tty/serial/8250/8250_core.c:681 |
| console_init+0x49d/0x6d3 kernel/printk/printk.c:2915 |
| start_kernel+0x5e9/0x879 init/main.c:713 |
| secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241 |
| |
| -> #0 (console_owner){....}-{0:0}: |
| [...] |
| lock_acquire+0x127/0x340 kernel/locking/lockdep.c:4734 |
| console_trylock_spinning kernel/printk/printk.c:1773 [inline] <-- lock(console_owner); |
| vprintk_emit+0x307/0x470 kernel/printk/printk.c:2023 |
| vprintk_func+0x8d/0x250 kernel/printk/printk_safe.c:394 |
| printk+0xba/0xed kernel/printk/printk.c:2084 |
| fail_dump lib/fault-inject.c:45 [inline] |
| should_fail+0x67b/0x7c0 lib/fault-inject.c:144 |
| __should_failslab+0x152/0x1c0 mm/failslab.c:33 |
| should_failslab+0x5/0x10 mm/slab_common.c:1224 |
| slab_pre_alloc_hook mm/slab.h:468 [inline] |
| slab_alloc_node mm/slub.c:2723 [inline] |
| slab_alloc mm/slub.c:2807 [inline] |
| __kmalloc+0x72/0x300 mm/slub.c:3871 |
| kmalloc include/linux/slab.h:582 [inline] |
| tty_buffer_alloc+0x23f/0x2a0 drivers/tty/tty_buffer.c:175 |
| __tty_buffer_request_room+0x156/0x2a0 drivers/tty/tty_buffer.c:273 |
| tty_insert_flip_string_fixed_flag+0x93/0x250 drivers/tty/tty_buffer.c:318 |
| tty_insert_flip_string include/linux/tty_flip.h:37 [inline] |
| pty_write+0x126/0x1f0 drivers/tty/pty.c:122 <-- lock(&port->lock); |
| n_tty_write+0xa7a/0xfc0 drivers/tty/n_tty.c:2356 |
| do_tty_write drivers/tty/tty_io.c:961 [inline] |
| tty_write+0x512/0x930 drivers/tty/tty_io.c:1045 |
| __vfs_write+0x76/0x100 fs/read_write.c:494 |
| [...] |
| |
| other info that might help us debug this: |
| |
| Chain exists of: |
| console_owner --> &port_lock_key --> &port->lock |
| |
| Link: https://lkml.kernel.org/r/20220511061951.1114-2-zhengqi.arch@bytedance.com |
| Link: https://lkml.kernel.org/r/20220510113809.80626-2-zhengqi.arch@bytedance.com |
| Fixes: b6da31b2c07c ("tty: Fix data race in tty_insert_flip_string_fixed_flag") |
| Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> |
| Acked-by: Jiri Slaby <jirislaby@kernel.org> |
| Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Cc: Akinobu Mita <akinobu.mita@gmail.com> |
| Cc: Vlastimil Babka <vbabka@suse.cz> |
| Cc: Steven Rostedt (Google) <rostedt@goodmis.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| drivers/tty/tty_buffer.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c |
| index dfccc102c1dd..e65faa98146e 100644 |
| --- a/drivers/tty/tty_buffer.c |
| +++ b/drivers/tty/tty_buffer.c |
| @@ -166,7 +166,8 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) |
| have queued and recycle that ? */ |
| if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit) |
| return NULL; |
| - p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC); |
| + p = kmalloc(sizeof(struct tty_buffer) + 2 * size, |
| + GFP_ATOMIC | __GFP_NOWARN); |
| if (p == NULL) |
| return NULL; |
| |
| -- |
| 2.35.1 |
| |