I am kind of lost trying to figure out how can kmallocs work if they
are called before kmem_cache_init
(e.g. such a case occurs when in start_kernel() we call
parse_early_param() (which in turn might call
early_serial8250_setup() if earlycon= is used in kernel command-line)
before mm_init() ?(which later calls
kmem_cache_init() )
From what I understood, kmalloc() (SLUB implementation) first tries to
find out the slab fit for the size
being kmalloced and slabs are nothing but kmalloc_caches[]. Now these
kmalloc_caches get initialized in
kmem_cache_init().
What am I missing here ?
Regards,
Sukanto Ghosh
--
Regards,
Sukanto Ghosh
From: Dave Hylands <hidden> Date: 2012-01-29 06:58:25
Hi Sukanto
On Sat, Jan 28, 2012 at 10:02 PM, Sukanto Ghosh
[off-list ref] wrote:
I am kind of lost trying to figure out how can kmallocs work if they
are called before kmem_cache_init
(e.g. such a case occurs when in start_kernel() we call
parse_early_param() (which in turn might call
early_serial8250_setup() if earlycon= is used in kernel command-line)
before mm_init() ?(which later calls
kmem_cache_init() )
I don't think that you're allowed to call kmalloc during early_setup.
I don't see where early_serial8250_setup calls kmalloc.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
Hi Dave,
If you look into start_kernel() the call to parse_early_param()
precedes mm_init().
parse_early_param() eventually calls do_early_param().
do_early_param() parses for "earlycon" in kernel commandline and then calls the
setup_function associated with earlycon.
I have in my commandline: earlycon=uart8250,mmio32,0x10000000,9600
Call flow starting from drivers/tty/serial/8250_early.c will lead to kmalloc
early_param("early_con", setup_early_serial8250_console)
setup_early_serial8250_console()
early_serial8250_setup()
parse_options()
ioremap_nocache()
... arch-specific-ioremap
-- some form of arch specific __ioremap_caller
--- get_vm_area_caller()
__get_vm_area_node
kzalloc_node
kmalloc_node
kmalloc
Regards,
Sukanto
On Jan 29, 2012 12:28 PM, "Dave Hylands" [off-list ref] wrote:
Hi Sukanto
On Sat, Jan 28, 2012 at 10:02 PM, Sukanto Ghosh
[off-list ref] wrote:
quoted
I am kind of lost trying to figure out how can kmallocs work if they
are called before kmem_cache_init
(e.g. such a case occurs when in start_kernel() we call
parse_early_param() (which in turn might call
early_serial8250_setup() if earlycon= is used in kernel command-line)
before mm_init() ?(which later calls
kmem_cache_init() )
I don't think that you're allowed to call kmalloc during early_setup.
I don't see where early_serial8250_setup calls kmalloc.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
From: Dave Hylands <hidden> Date: 2012-01-29 09:33:37
Hi Sukanto,
On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh
[off-list ref] wrote:
Hi Dave,
If you look into start_kernel() the call to parse_early_param()
precedes mm_init().
parse_early_param() eventually calls do_early_param().
do_early_param() parses for "earlycon" in kernel commandline and then calls the
setup_function associated with earlycon.
I have in my commandline: earlycon=uart8250,mmio32,0x10000000,9600
Call flow starting from drivers/tty/serial/8250_early.c will lead to kmalloc
early_param("early_con", setup_early_serial8250_console)
? setup_early_serial8250_console()
? ? ? early_serial8250_setup()
? ? ? ? ? parse_options()
? ? ? ? ? ? ? ioremap_nocache()
? ? ? ? ? ? ? ? ?... arch-specific-ioremap
? ? ? ? ? ? ? ? ? ? ? ?-- some form of arch specific __ioremap_caller
? ? ? ? ? ? ? ? ? ? ? ? ? ?--- get_vm_area_caller()
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?__get_vm_area_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? kzalloc_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? kmalloc_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?kmalloc
It looks like CONFIG_FIX_EARLYCON_MEM defaults to y (on x86 anyways),
so this would cause the path that doesn't call ioremam_nocache to be
taken.
I'm guessing that if you specify earycon, then you also need to ensure
that CONFIG_FIX_EARLYCON is set.
You didn't mention which architecture you were using. ARM has an
early_printk which is sort of like an early console.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
So to use a MMIO based 8250 as "earlycon", either we need to have some
sort of fixmap
(as in case of x86) or otherwise we need to have a ioremap_nocache()
version that works
even before kmem_cache_init() is called.
I am not sure how many architectures will have such form of ioremap
other than maybe
nommu variants.
Greg,
Has anyone used the ioremap path so far ? If not, then why have it
there as usual ioremap
can be used only after mm_init(), but this driver whenever used will
get called earlier than that ?
Regards,
Sukanto
On Sun, Jan 29, 2012 at 3:03 PM, Dave Hylands [off-list ref] wrote:
Hi Sukanto,
On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh
[off-list ref] wrote:
quoted
Hi Dave,
If you look into start_kernel() the call to parse_early_param()
precedes mm_init().
parse_early_param() eventually calls do_early_param().
do_early_param() parses for "earlycon" in kernel commandline and then calls the
setup_function associated with earlycon.
I have in my commandline: earlycon=uart8250,mmio32,0x10000000,9600
Call flow starting from drivers/tty/serial/8250_early.c will lead to kmalloc
early_param("early_con", setup_early_serial8250_console)
? setup_early_serial8250_console()
? ? ? early_serial8250_setup()
? ? ? ? ? parse_options()
? ? ? ? ? ? ? ioremap_nocache()
? ? ? ? ? ? ? ? ?... arch-specific-ioremap
? ? ? ? ? ? ? ? ? ? ? ?-- some form of arch specific __ioremap_caller
? ? ? ? ? ? ? ? ? ? ? ? ? ?--- get_vm_area_caller()
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?__get_vm_area_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? kzalloc_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? kmalloc_node
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?kmalloc
It looks like CONFIG_FIX_EARLYCON_MEM defaults to y (on x86 anyways),
so this would cause the path that doesn't call ioremam_nocache to be
taken.
I'm guessing that if you specify earycon, then you also need to ensure
that CONFIG_FIX_EARLYCON is set.
You didn't mention which architecture you were using. ARM has an
early_printk which is sort of like an early console.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com
So to use a MMIO based 8250 as "earlycon", either we need to have some
sort of fixmap
(as in case of x86) or otherwise we need to have a ioremap_nocache()
version that works
even before kmem_cache_init() is called.
I am not sure how many architectures will have such form of ioremap
other than maybe
nommu variants.
Some architectures check for mem_init_done.
Probably every architecture must provide an "early_ioremap" function to
be used in early _code_.
Greg,
Has anyone used the ioremap path so far ? If not, then why have it
there as usual ioremap
can be used only after mm_init(), but this driver whenever used will
get called earlier than that ?
Regards,
Sukanto
On Sun, Jan 29, 2012 at 3:03 PM, Dave Hylands[off-list ref] wrote:
quoted
Hi Sukanto,
On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh
[off-list ref] wrote:
quoted
Hi Dave,
If you look into start_kernel() the call to parse_early_param()
precedes mm_init().
parse_early_param() eventually calls do_early_param().
do_early_param() parses for "earlycon" in kernel commandline and then calls the
setup_function associated with earlycon.
I have in my commandline: earlycon=uart8250,mmio32,0x10000000,9600
Call flow starting from drivers/tty/serial/8250_early.c will lead to kmalloc
early_param("early_con", setup_early_serial8250_console)
setup_early_serial8250_console()
early_serial8250_setup()
parse_options()
ioremap_nocache()
... arch-specific-ioremap
-- some form of arch specific __ioremap_caller
--- get_vm_area_caller()
__get_vm_area_node
kzalloc_node
kmalloc_node
kmalloc
It looks like CONFIG_FIX_EARLYCON_MEM defaults to y (on x86 anyways),
so this would cause the path that doesn't call ioremam_nocache to be
taken.
I'm guessing that if you specify earycon, then you also need to ensure
that CONFIG_FIX_EARLYCON is set.
You didn't mention which architecture you were using. ARM has an
early_printk which is sort of like an early console.
--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com