serial: pl011: Fix lockdep splat when handling magic-sysrq interrupt
commit 534cf755d9
upstream.
Issuing a magic-sysrq via the PL011 causes the following lockdep splat,
which is easily reproducible under QEMU:
| sysrq: Changing Loglevel
| sysrq: Loglevel set to 9
|
| ======================================================
| WARNING: possible circular locking dependency detected
| 5.9.0-rc7 #1 Not tainted
| ------------------------------------------------------
| systemd-journal/138 is trying to acquire lock:
| ffffab133ad950c0 (console_owner){-.-.}-{0:0}, at: console_lock_spinning_enable+0x34/0x70
|
| but task is already holding lock:
| ffff0001fd47b098 (&port_lock_key){-.-.}-{2:2}, at: pl011_int+0x40/0x488
|
| which lock already depends on the new lock.
[...]
| Possible unsafe locking scenario:
|
| CPU0 CPU1
| ---- ----
| lock(&port_lock_key);
| lock(console_owner);
| lock(&port_lock_key);
| lock(console_owner);
|
| *** DEADLOCK ***
The issue being that CPU0 takes 'port_lock' on the irq path in pl011_int()
before taking 'console_owner' on the printk() path, whereas CPU1 takes
the two locks in the opposite order on the printk() path due to setting
the "console_owner" prior to calling into into the actual console driver.
Fix this in the same way as the msm-serial driver by dropping 'port_lock'
before handling the sysrq.
Cc: <stable@vger.kernel.org> # 4.19+
Cc: Russell King <linux@armlinux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20200811101313.GA6970@willie-the-truck
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Tested-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200930120432.16551-1-will@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
parent
44ef3b63c7
commit
870d910e1a
|
@ -313,8 +313,9 @@ static void pl011_write(unsigned int val, const struct uart_amba_port *uap,
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*/
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static int pl011_fifo_to_tty(struct uart_amba_port *uap)
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{
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u16 status;
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unsigned int ch, flag, fifotaken;
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int sysrq;
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u16 status;
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for (fifotaken = 0; fifotaken != 256; fifotaken++) {
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status = pl011_read(uap, REG_FR);
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@ -349,10 +350,12 @@ static int pl011_fifo_to_tty(struct uart_amba_port *uap)
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flag = TTY_FRAME;
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}
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if (uart_handle_sysrq_char(&uap->port, ch & 255))
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continue;
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spin_unlock(&uap->port.lock);
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sysrq = uart_handle_sysrq_char(&uap->port, ch & 255);
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spin_lock(&uap->port.lock);
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uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag);
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if (!sysrq)
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uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag);
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}
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return fifotaken;
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