Hi,
This is regarding an Oops message that I get in my segment
tracker LKM, even after setting up the Kernels Page tables.
On trying to read segment information by ioctl calls to a
device,by feeding structured information from user_space, for a
"process by name" lookup, I find that my Code is Oopsing,while
trying to copy the information from the Process Virtual address
space,after setting up the Kernels Page tables.
I have a vmalloced segment in kernel space where I copy the
Process segment information ,before moving that into user_space
with a copy_to_user. I copy all the segments by looping through
the vm_area_struct fields (vm_next), and copying them up into
user_space. Before copying,I do the page table hooks in the kernel
space, to make it point to the Processes PTE entry for its
segments virtual address.
The code is Oopsing at the point where I try to Copy the processes
segment into the vmalloc buffer.
Infact it works,if I try to copy a single Segment
{code,stack,data} worth 2 pages into the user_space structure.
Whats the reason for the Oops,inspite of the Page table hooks?
(Note:In my quest,I dont corrupt the Kernels Page table
Entry,because I save and restore the old entry after the copy
operation.)
BTW, if anybody has gone inside A.Rubinis "sbull" code for Linux
Device Drivers,he will find a "spinlock" on a "vmalloc" call.
I have a hunch that its buggy,as "get_vm_area" in "mm/vmalloc.c"
miiiight sleep on a call to "kmalloc" with a GFP_KERNEL.
I have rewritten the "sbull" partition{less} devices with a
"semaphore" on a vmalloc and a spinlock before a io_transfer, for
a 2.2.x.
Any suggestions,in favour or against A.Rubinis "spinlock" approach
would be appreciated.
I am betting on a "A.Rubini" __sleep__ before a "spinlock" on a
"vmalloc" call.
Regards,
-Karthick
(http://kernelnewbies.org/wiki/moin.cgi/Karthick
Doesnt Work !!. Try a google.com lookup on "a.r.karthick" and
take on the Googles Cache for the URL-Should find 2.4 Linux Kernel
Internals,Incomplete for a Review.)
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