Date:	Tue, 11 Mar 2008 22:59:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Gordon Farquharson" <gordonfarquharson@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org
Subject: Re: physmap and "request_module: runaway loop modprobe net-pf-1"

On Tue, 11 Mar 2008 23:35:28 -0600 "Gordon Farquharson" <gordonfarquharson@...il.com> wrote:

> Hi All

Let's cc the MTD list.

> On machines that register a physmap flash platform device (e.g. many
> arm machines), parse_mtd_partitions() in drivers/mtd/mtdpart.c can
> cause the following output in the boot log:
> 
> request_module: runaway loop modprobe net-pf-1
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> 
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> 
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> ...
> 
> To illustrate how this can occur, I'll use the example where
> CONFIG_KMOD=y, CONFIG_MTD_PARTITIONS=y, CONFIG_MTD_REDBOOT_PARTS=y,
> and CONFIG_CMDLINE_PARTS is not set. I'll also refer to the following
> code segment which is in drivers/mtd/mtdpart.c:parse_mtd_partitions():
> 
> 	for ( ; ret <= 0 && *types; types++) {
> 		parser = get_partition_parser(*types);
> #ifdef CONFIG_KMOD
> 		if (!parser && !request_module("%s", *types))
> 				parser = get_partition_parser(*types);
> #endif
> 		if (!parser) {
> 			printk(KERN_NOTICE "%s partition parsing not available\n",
> 			       *types);
> 			continue;
> 		}
> 		ret = (*parser->parse_fn)(master, pparts, origin);
> 		if (ret > 0) {
> 			printk(KERN_NOTICE "%d %s partitions found on MTD device %s\n",
> 			       ret, parser->name, master->name);
> 		}
> 		put_partition_parser(parser);
> 	}
> 
> I should note that I am assuming (because I don't understand how) that
> request_module() requires net-pf-1 to succeed. This assumption is
> based on my observation of the request_module message
> ("request_module: runaway loop modprobe net-pf-1"), and that
> af_unix_init() (net-pf-1 initialization) is called only after the call
> to request_module() in this example.
> 
> Based on the configuration and assumptions described above, the
> sequence of events that cause the boot log messages above are:
> 
> 1. the first call to get_partition_parser() in parse_mtd_partitions()
> does not find the parser in the the list of registered parsers, i.e.
> get_partition_parser() returns a NULL pointer. In this example, the
> only registered parser in the list is called Redboot;
> 
> 2. parse_mtd_partitions() calls request_module() with (in this
> example) the parameter "cmdlinepart";
> 
> 3. request_module() complains (request_module: runaway loop modprobe
> net-pf-1, etc.) because af_unix_init() has not been called. The boot
> log shows that af_unix_init() is called only after
> parse_mtd_partitions() finishes.
> 
> register_mtd_parser: RedBoot
> physmap platform flash device: 00080000 at f0000000
> Found: ST M29W400DB
> physmap-flash.0: Found 1 x16 devices at 0x0 in 16-bit bank
> number of JEDEC chips: 1
> cfi_cmdset_0002: Disabling erase-suspend-program due to code brokenness.
> parse_mtd_partitions:
> get_partition_parser: name=cmdlinepart
> get_partition_parser: p->name=RedBoot
> get_partition_parser: p->owner=00000000
> get_partition_parser: ret=00000000
> parse_mtd_partitions: cmdlinepart
> request_module: runaway loop modprobe net-pf-1
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> 
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> 
> modprobe: FATAL: Could not load
> /lib/modules/2.6.25-rc4-iop32x/modules.dep: No such file or directory
> 
> <--- 47 repeated modprobe messages deleted --->
> parse_mtd_partitions: request_module called
> cmdlinepart partition parsing not available
> get_partition_parser: name=RedBoot
> get_partition_parser: p->name=RedBoot
> get_partition_parser: p->owner=00000000
> get_partition_parser: ret->name=RedBoot
> get_partition_parser: ret=c02b0f8c
> parse_mtd_partitions: RedBoot
> parse_mtd_partitions: request_module called
> Searching for RedBoot partition table in physmap-flash.0 at offset 0x70000
> No RedBoot partition table detected in physmap-flash.0
> parse_mtd_partitions: end of function
> mice: PS/2 mouse device common for all mice
> i2c /dev entries driver
> rtc-rs5c372 0-0032: rs5c372a found, 24hr, driver version 0.5
> rtc-rs5c372 0-0032: rtc core: registered rtc-rs5c372 as rtc0
> iop-adma iop-adma.0: Intel(R) IOP: ( cpy intr )
> iop-adma iop-adma.1: Intel(R) IOP: ( cpy intr )
> NET: Registered protocol family 26
> TCP bic registered
> af_unix_init:
> NET: Registered protocol family 1
> NET: Registered protocol family 17
> XScale DSP coprocessor detected.
> registered taskstats version 1
> rtc-rs5c372 0-0032: setting system clock to 2008-03-11 03:16:46 UTC (1205205406)
> 
> The reason parse_mtd_partitions() tries to use cmdlinepart, even
> though it is not a registered parsing scheme when CONFIG_CMDLINE_PARTS
> is not set, is because cmdlinepart is hard coded in
> drivers/mtd/maps/physmap.c:
> 
> #ifdef CONFIG_MTD_PARTITIONS
> static const char *part_probe_types[] = { "cmdlinepart", "RedBoot", NULL };
> #endif
> 
> The simple solution to eliminating the messages in the boot log
> appears to be to ensure that, for machines that use a physmap flash
> device, CONFIG_MTD_REDBOOT_PARTS and CONFIG_CMDLINE_PARTS are set if
> CONFIG_MTD_PARTITIONS is set. However, the problem also occurs if
> CONFIG_MTD_REDBOOT_PARTS is configured to be built as a module,
> because again, request_module() fails because af_unix_init() has not
> been called.
> 
> It would be simpler if all parsing code could only be built into the
> kernel. In this case, built in parsers would be registered by the time
> parse_mtd_partitions() is called, so the call to request_module() in
> parse_mtd_partitions() could be removed:
> 
> #ifdef CONFIG_KMOD
> 		if (!parser && !request_module("%s", *types))
> 				parser = get_partition_parser(*types);
> #endif
> 
> This solution would require simply changing the parser configuration
> options to bool in drivers/mtd/Kconfig. Is there a reason to allow the
> parsing code to be built as a module?

That sounds reasonable.

> Alternatively, if selecting CONFIG_MTD_PARTITIONS and not selecting
> both CONFIG_MTD_REDBOOT_PARTS and CONFIG_CMDLINE_PARTS, or selecting
> CONFIG_MTD_PARTITIONS and not selecting CONFIG_CMDLINE_PARTS and
> selecting CONFIG_MTD_REDBOOT_PARTS as a module, are valid
> configurations, it seems that parse_mtd_partitions() must be called
> only after af_unix_init() has been called. Is this possible?

Probably.

We can specify the order in which these things are called at compile-time. 
See these, from include/linux/init.h:

#define core_initcall(fn)		__define_initcall("1",fn,1)
#define postcore_initcall(fn)		__define_initcall("2",fn,2)
#define arch_initcall(fn)		__define_initcall("3",fn,3)
#define subsys_initcall(fn)		__define_initcall("4",fn,4)
#define fs_initcall(fn)			__define_initcall("5",fn,5)
#define rootfs_initcall(fn)		__define_initcall("rootfs",fn,rootfs)
#define device_initcall(fn)		__define_initcall("6",fn,6)
#define late_initcall(fn)		__define_initcall("7",fn,7)

Now, af_unix_init() uses module_init(), which is really __initcall(), which
is really device_initcall() (ug, don't ask).

So you can do what you're sugesting here by locating the caller/callers of
parse_mtd_partitions() and marking them late_initcall().

> Lastly, does anybody care because this problem does not cause the
> kernel to crash? :-)

We're very caring people.

I'd suggest that you make your own decision as to what is the best fix, then
send a patch.  Please cc me on it and I'll make sure that it gets
appropriately handled.  This may take a bit of time, as the MTD patch
backlog is rather large at present.

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