Hello,
I'm trying to debug an issue I'm encountering on kernel 3.4 in the android binder.
Basically in the function binder_update_page_range it allocates a page. If I
understand correctly the next part, it maps this page_addr to the page in kernel
space and then maps the user process addr to the same page.
If I attempt to use virt_to_head_page(page_addr) after all this is accomplished, I
should get back the page that was just allocated and mapped, but that's not what
I observe on my system as seen in the log below.
[ 20.960786] ( 25.557586) binder_open: 219:219
[ 20.960827] ( 25.557617) binder_ioctl: 219:219 c0046209 be9a7938
[ 20.960841] ( 25.557617) binder_ioctl: 219:219 40046205 be9a793c
[ 20.960857] ( 25.557647) binder_mmap: 219 b6c02000-b6d00000 (1016 K) vma 200071 pagep 79f
[ 20.960907] ( 25.557708) binder: 219: allocate pages cb300000-cb301000
*** binder allocated page here (nil == first_page value)
[ 20.960922] ( 25.557708) binder: page_alloc cd958238 (nil)
*** dump of the page
[ 20.960931] ( 25.557708) page:cd958238 count:1 mapcount:0 mapping: (nil) index:0x0
[ 20.960939] ( 25.557739) page flags: 0x0()
*** first attempt of virt_to_head_page(page_addr) before kernel mapping + dump of returned page
*** which shows it's uninitialized (aaaaaaaa = first_page value)
[ 20.960947] ( 25.557739) virt_to_head_page cd392c00
[ 20.960955] ( 25.557739) compound_head_by_tail cd392c00 aaaaaaaa
[ 20.960965] ( 25.557769) page:cd392c00 count:-1431655766 mapcount:-1431655765 mapping:aaaaaaaa index:0xaaaaaaaa
[ 20.960973] ( 25.557769) page flags: 0xaaaaaaaa(error|uptodate|lru|slab|arch_1|private|writeback|tail|mappedtodisk|swapbacked|mlocked)
[ 20.960981] ( 25.557769) virt_to_head_page cd9681bc
[ 20.960997] ( 25.557800) virt_to_head_page cd967c1c
*** before kernel + user space mapping calls
[ 20.961551] ( 25.558349) binder: addr cb300000 page aaaaaaaa
*** after kernel + user space mapping calls - dump allocated page again
[ 20.961566] ( 25.558349) page:cd958238 count:2 mapcount:1 mapping: (nil) index:0x0
[ 20.961574] ( 25.558380) page flags: 0x200(arch_1)
*** second attempt of virt_to_head_page(page_addr) expecting
*** that allocated page above would be mapped to this address
[ 20.961584] ( 25.558380) binder: addr cb300000 page aaaaaaaa
[ 20.961595] ( 25.558380) binder: 219: add free buffer, size 1040344, at cb300000
[ 20.961605] ( 25.558410) binder_mmap: 219 b6c02000-b6d00000 maps cb300000
…
Blows up on invalid page access 'aaaaaaaa' a while later.
Thanks
David
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