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serial: core: introduce guard(uart_port_lock_check_sysrq_irqsave) 

uart_handle_break() and uart_prepare_sysrq_char() (in
include/linux/serial_core.h) capture a SysRq character into
port->sysrq_ch while the port lock is held and rely on the unlock
helper -- uart_unlock_and_check_sysrq_irqrestore() -- to dispatch the
captured character to handle_sysrq() on scope exit.

The existing guard(uart_port_lock_irqsave) cannot be used by IRQ
handlers that process RX, because its destructor calls plain
uart_port_unlock_irqrestore() and silently drops port->sysrq_ch.

Add a dedicated guard(uart_port_lock_check_sysrq_irqsave) variant
whose destructor is the sysrq-aware unlock helper. The lock side is
identical to uart_port_lock_irqsave -- only the unlock-time behaviour
differs. Callers that may capture SysRq characters must use
guard(uart_port_lock_check_sysrq_irqsave); the existing
guard(uart_port_lock_irqsave) keeps its current plain-unlock semantics
for the many callers that do not process RX.

The new macro is placed after the CONFIG_MAGIC_SYSRQ_SERIAL block so
both definitions of uart_unlock_and_check_sysrq_irqrestore() (sysrq
enabled and disabled) are visible at expansion time. When
CONFIG_MAGIC_SYSRQ_SERIAL=n the destructor degenerates to plain
uart_port_unlock_irqrestore(), so there is no overhead.

No functional change on its own; users are converted in the following
patches.

Cc: stable@vger.kernel.org
Signed-off-by: Jacques Nilo <jnilo@free.fr>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/3849af4bc55d5d2a424fa850844e94d641b2f8a6.1778675349.git.jnilo@free.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
master
Jacques Nilo 2026-05-13 15:30:23 +02:00 committed by Greg Kroah-Hartman
parent a3bb136bff
commit c3cce2e67b
1 changed files with 12 additions and 0 deletions
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12
include/linux/serial_core.h
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@ -1274,6 +1274,18 @@ static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port
}
#endif /* CONFIG_MAGIC_SYSRQ_SERIAL */
/*
* Variant of guard(uart_port_lock_irqsave) for IRQ handlers that may capture
* a SysRq character via uart_prepare_sysrq_char(). The destructor uses the
* sysrq-aware unlock helper so that a captured port->sysrq_ch is dispatched
* to handle_sysrq() on scope exit. The plain guard variant silently drops
* sysrq_ch and must not be used by callers that process RX.
*/
DEFINE_LOCK_GUARD_1(uart_port_lock_check_sysrq_irqsave, struct uart_port,
uart_port_lock_irqsave(_T->lock, &_T->flags),
uart_unlock_and_check_sysrq_irqrestore(_T->lock, _T->flags),
unsigned long flags);
/*
* We do the SysRQ and SAK checking like this...
*/