I've seen UML 2.6.21-rc crashing at boot due to CONFIG_DEBUG_SHIRQ. Below I've
written the diagnosis, without a resolution.
The problem is in mconsole_init() with CONFIG_DEBUG_SHIRQ - it registers the
mconsole IRQ. CONFIG_DEBUG_SHIRQ triggers a fake IRQ at registration time, to
catch device drivers not yet ready to handle the IRQ - but our
mconsole_interrupt() handler calls recvfrom which never returns, after
creating the socket.
This was introduced (as debug stuff) in commit
a304e1b82808904c561b7b149b467e338c53fcce.
I thought that it was correct for UML to do this - but I just realized that
SHIRQ means exactly that another device may register together with us, so
spurious IRQs may happen coming from the other device. The fix is to remove
IRQF_SHARED from registration, since it's not needed.
However, this cannot be done for other IRQs which may actually be shared, like
the console IRQ (which is shared among multiple consoles). I noted this on an
UML where only one getty is started, which is strange, however this message
convinced me (just at a glance) that multiple IRQ were being registered.
IRQ handler type mismatch for IRQ 2
current handler: console
Call Trace:
60fd3b78: [<6004ce5a>] setup_irq+0x1b2/0x1cf
60fd3ba8: [<600133c4>] line_interrupt+0x0/0x26
60fd3bb8: [<6004d06b>] request_irq+0xdc/0xfd
60fd3bf8: [<6000d049>] um_request_irq+0x25/0x47
60fd3c28: [<600139c8>] line_setup_irq+0x47/0x93
60fd3c78: [<6001262c>] enable_chan+0x4b/0x59
60fd3c98: [<60013a7a>] line_open+0x66/0xeb
60fd3cc8: [<600120aa>] con_open+0x11/0x13
60fd3cd8: [<60108cf6>] tty_open+0x14f/0x2ba
The proper fix there may be to avoid blocking on read (i.e. using
O_NONBLOCK) - and in that case I'd suggest deferring it since it does not
seem me a bug which can be actually hit.
However, I'm not sure about this. What do you think, Jeff?
Mconsole backtrace:
(gdb) where
#0 0x000000006017d165 in __recvfrom_nocancel () at swab.h:134
#1 0x00000000600186d7 in mconsole_get_request (fd=7, req=0x602e3ac0)
at
/home/paolo/Admin/kernel/6/VCS/linux-2.6.git/arch/um/drivers/mconsole_user.c:90
#2 0x00000000600175aa in mconsole_interrupt (irq=7, dev_id=0x602e3b50) at
list.h:50
#3 0x000000006004d04d in request_irq (irq=9, handler=0x60017501
<mconsole_interrupt>, irqflags=1, devname=0x60218252 "mconsole", dev_id=0x7)
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/kernel/irq/manage.c:550
#4 0x000000006000d049 in um_request_irq (irq=9, fd=7, type=0,
handler=0x602e3b50 <req.1+144>, irqflags=524, devname=0xffffffffffffffff
<Address 0xffffffffffffffff out of bounds>,
dev_id=0x7)
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/arch/um/kernel/irq.c:374
#5 0x00000000600183c7 in mconsole_init ()
at
/home/paolo/Admin/kernel/6/VCS/linux-2.6.git/arch/um/drivers/mconsole_kern.c:817
#6 0x00000000600007fb in do_initcalls ()
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/init/main.c:672
#7 0x00000000600008d4 in do_basic_setup ()
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/init/main.c:712
#8 0x000000006000094d in init (unused=0x7)
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/init/main.c:803
#9 0x000000006001e77b in run_kernel_thread (fn=0x600008e6 <init>, arg=0x0,
jmp_ptr=0x20c)
at /home/paolo/Admin/kernel/6/VCS/linux-2.6.git/arch/um/os-Linux/process.c:292
#10 0x0000000060011343 in new_thread_handler () at thread_info.h:46
Original commit:
Commit: a304e1b82808904c561b7b149b467e338c53fcce
Author: David Woodhouse <[EMAIL PROTECTED]> Mon, 12 Feb 2007 00:52:00 -0800
[PATCH] Debug shared irqs
Drivers registering IRQ handlers with SA_SHIRQ really ought to be able to
handle an interrupt happening before request_irq() returns. They also
ought to be able to handle an interrupt happening during the start of
their
call to free_irq(). Let's test that hypothesis....
--
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
Various other bogus IRQF_SHARED removals. The console IRQ is actually shared
with itself on other consoles, the network IRQ may be shared with other network
interfaces,
Index: linux-2.6.git/arch/um/drivers/line.c
===================================================================
--- linux-2.6.git.orig/arch/um/drivers/line.c
+++ linux-2.6.git/arch/um/drivers/line.c
@@ -404,7 +404,7 @@ static irqreturn_t line_write_interrupt(
int line_setup_irq(int fd, int input, int output, struct line *line, void *data)
{
const struct line_driver *driver = line->driver;
- int err = 0, flags = IRQF_DISABLED | IRQF_SHARED | IRQF_SAMPLE_RANDOM;
+ int err = 0, flags = IRQF_DISABLED | IRQF_SAMPLE_RANDOM;
if (input)
err = um_request_irq(driver->read_irq, fd, IRQ_READ,
@@ -803,7 +803,7 @@ void register_winch_irq(int fd, int tty_
spin_unlock(&winch_handler_lock);
if(um_request_irq(WINCH_IRQ, fd, IRQ_READ, winch_interrupt,
- IRQF_DISABLED | IRQF_SHARED | IRQF_SAMPLE_RANDOM,
+ IRQF_DISABLED | IRQF_SAMPLE_RANDOM,
"winch", winch) < 0)
printk("register_winch_irq - failed to register IRQ\n");
}
Index: linux-2.6.git/arch/um/drivers/net_kern.c
===================================================================
--- linux-2.6.git.orig/arch/um/drivers/net_kern.c
+++ linux-2.6.git/arch/um/drivers/net_kern.c
@@ -128,7 +128,7 @@ static int uml_net_open(struct net_devic
}
err = um_request_irq(dev->irq, lp->fd, IRQ_READ, uml_net_interrupt,
- IRQF_DISABLED | IRQF_SHARED, dev->name, dev);
+ IRQF_DISABLED, dev->name, dev);
if(err != 0){
printk(KERN_ERR "uml_net_open: failed to get irq(%d)\n", err);
err = -ENETUNREACH;
uml: make various UML not shared
If another device shared the IRQ with this one we could get spurious IRQs. Since
mconsole_interrupt() calls recvfrom() and hangs when no message is received,
this is bogus.
In fact, under CONFIG_DEBUG_SHIRQ, it causes an hang at boot.
Likewise, various other IRQs cause similar hang, but those IRQ can be actually
shared.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <[EMAIL PROTECTED]>
Index: linux-2.6.git/arch/um/drivers/mconsole_kern.c
===================================================================
--- linux-2.6.git.orig/arch/um/drivers/mconsole_kern.c
+++ linux-2.6.git/arch/um/drivers/mconsole_kern.c
@@ -815,7 +815,7 @@ static int mconsole_init(void)
register_reboot_notifier(&reboot_notifier);
err = um_request_irq(MCONSOLE_IRQ, sock, IRQ_READ, mconsole_interrupt,
- IRQF_DISABLED | IRQF_SHARED | IRQF_SAMPLE_RANDOM,
+ IRQF_DISABLED | IRQF_SAMPLE_RANDOM,
"mconsole", (void *)sock);
if (err){
printk("Failed to get IRQ for management console\n");
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