fix serial close hang
PATCH 1/1 fix serial close hang
Hi,
2.4/2.5 kernels suffer from an infinitely long hang when a serial tty device is closed, and there are characters waiting to be sent. The hang occurs in tty_wait_until_sent.
There is a timeout 'closing_wait' which defines how long to wait for the TX buffers to empty; the problem is that the serial layer totally ignores it. It is stored in two structures, 'info' and 'state'. It is initialised in the 'state' structure, but used from the 'info' structure.
It turns out that 'hub6' was also missing.
I'm not currently clear what the expected behaviour should be when the timeout is changed via setserial, and others have the port open - I've opted to preserve the timeout until all users close the port. It's trivial to change this behaviour though.
Comments welcome.
include/linux/serialP.h +1 -1
@@ -70,7 +70,7 @@int x_char;/* xon/xoff character */ int close_delay;unsigned short closing_wait; -unsigned short closing_wait2; +unsigned short closing_wait2;/* obsolete */ int IER ;/* Interrupt Enable Register */ int MCR ;/* Modem control register */ int LCR ;/* Line control register */
drivers/char/serial.c +27 -11
@@ -3095,36 +3095,52 @@ sstate = rs_table + line; sstate->count++; -if (sstate->info) { - *ret_info = sstate->info; -return 0 ; - } + info = sstate->info; + +/* +* If the async_struct is already allocated, do the fastpath. +*/ +if (info) + goto out; + info =kmalloc (sizeof (struct async_struct ),GFP_KERNEL );if (!info) { sstate->count--;return -ENOMEM ; } +memset (info,0 ,sizeof (struct async_struct ));init_waitqueue_head (&info->open_wait);init_waitqueue_head (&info->close_wait);init_waitqueue_head (&info->delta_msr_wait); info->magic =SERIAL_MAGIC ; info->port = sstate->port; + info->hub6 = sstate->hub6; info->flags = sstate->flags; - info->io_type = sstate->io_type; - info->iomem_base = sstate->iomem_base; - info->iomem_reg_shift = sstate->iomem_reg_shift; info->xmit_fifo_size = sstate->xmit_fifo_size; + info->state = sstate; info->line = line; + info->iomem_base = sstate->iomem_base; + info->iomem_reg_shift = sstate->iomem_reg_shift; + info->io_type = sstate->io_type; info->tqueue.routine = do_softint; info->tqueue.data = info; - info->state = sstate; +if (sstate->info) {kfree (info); - *ret_info = sstate->info; -return 0 ; + info = state->info; + }else { + sstate->info = info; + } + +out: +/* +* If this is the first open, copy over some timeouts. +*/ +if (sstate->count ==1 ) { + info->closing_wait = sstate->closing_wait; } - *ret_info = sstate->info = info; + *ret_info = info;return 0 ; }
Signature · 2 lines
Russell King ([email protected]) The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html
Quoted 1 line · Russell King
Comments welcome.
Patch applies flawlessly to 2.4.17, however compilation fails:
[....]
make[2]: Leaving directory /usr/src/linux/drivers/cdrom' make -C char modules
make[2]: Entering directory /usr/src/linux/drivers/char'
gcc -D__KERNEL__ -I/usr/src/linux/include -Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fomit-frame-pointer -fno-strict-aliasing -fno-common
-pipe -mpreferred-stack-boundary=2 -march=k6 -DMODULE -DEXPORT_SYMTAB -cserial.cserial.c: In function get_async_struct':
serial.c:3131: state' undeclared (first use in this function) serial.c:3131: (Each undeclared identifier is reported only once serial.c:3131: for each function it appears in.)
make[2]: *** [serial.o] Error 1
make[2]: Leaving directory /usr/src/linux/drivers/char' make[1]: *** [_modsubdir_char] Error 2
make[1]: Leaving directory /usr/src/linux/drivers'
make: *** [_mod_drivers] Error 2
elfie:/usr/src/linux #
Signature · 1 line
# Heinz Diehl, 68259 Mannheim, Germany
Quoted 1 line · Heinz Diehl
serial.c:3131: state' undeclared (first use in this function)
Whoops. This should fix it.
include/linux/serialP.h +1 -1
@@ -70,7 +70,7 @@int x_char;/* xon/xoff character */ int close_delay;unsigned short closing_wait; -unsigned short closing_wait2; +unsigned short closing_wait2;/* obsolete */ int IER ;/* Interrupt Enable Register */ int MCR ;/* Modem control register */ int LCR ;/* Line control register */
drivers/char/serial.c +27 -11
@@ -3095,36 +3095,52 @@ sstate = rs_table + line; sstate->count++; -if (sstate->info) { - *ret_info = sstate->info; -return 0 ; - } + info = sstate->info; + +/* +* If the async_struct is already allocated, do the fastpath. +*/ +if (info) + goto out; + info =kmalloc (sizeof (struct async_struct ),GFP_KERNEL );if (!info) { sstate->count--;return -ENOMEM ; } +memset (info,0 ,sizeof (struct async_struct ));init_waitqueue_head (&info->open_wait);init_waitqueue_head (&info->close_wait);init_waitqueue_head (&info->delta_msr_wait); info->magic =SERIAL_MAGIC ; info->port = sstate->port; + info->hub6 = sstate->hub6; info->flags = sstate->flags; - info->io_type = sstate->io_type; - info->iomem_base = sstate->iomem_base; - info->iomem_reg_shift = sstate->iomem_reg_shift; info->xmit_fifo_size = sstate->xmit_fifo_size; + info->state = sstate; info->line = line; + info->iomem_base = sstate->iomem_base; + info->iomem_reg_shift = sstate->iomem_reg_shift; + info->io_type = sstate->io_type; info->tqueue.routine = do_softint; info->tqueue.data = info; - info->state = sstate; +if (sstate->info) {kfree (info); - *ret_info = sstate->info; -return 0 ; + info = sstate->info; + }else { + sstate->info = info; + } + +out: +/* +* If this is the first open, copy over some timeouts. +*/ +if (sstate->count ==1 ) { + info->closing_wait = sstate->closing_wait; } - *ret_info = sstate->info = info; + *ret_info = info;return 0 ; }
Signature · 2 lines
Russell King ([email protected]) The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html
Quoted 1 line · Russell King
Whoops. This should fix it.
Yes, it does. The patch runs perfectly under 2.4.17.
Signature · 1 line
# Heinz Diehl, 68259 Mannheim, Germany