On Sun, May 6, 2018 at 3:52 AM, Daniel Danzberger <dan...@dd-wrt.com> wrote: > MMAP'ed memory that has been allocated via 'get_zeroed_page(GFP_KERNEL)' or > 'vmalloc()' doesn't always contain the same data when accessed from userspace. > > This means all userspace programs using mmap to access kernel memory aren't > always working properly on the Rambutan board. I am currently testing if other > ar71xx devices are affected as well. > > I first noticed this when using ALSA's mmap api to capture audio. > > Here is the feed for a kmod + userpace util to reproduce the issue: > g...@github.com:dddaniel/mmaptest.git > > The kernel module simply allocates a page and initializes it with 0xff. > The userspace application then mmap's and reads this page 10 times with a > 500ms > delay an checks if all data is 0xff. > > --- > root@OpenWrt:/# mmaptest-user > mmap addr: 0x77a04000 > [ 760.464968] mmap page 7573000 at va 87573000 > check memory ...FAIL (at byte 0) > check memory ...FAIL (at byte 96) > check memory ...FAIL (at byte 96) > check memory ...FAIL (at byte 96) > check memory ...FAIL (at byte 128) > --- > > I have no idea whats causing it. Does anybody have a hint on how to fix this ? > Try reverting https://github.com/torvalds/linux/commit/c00ab4896ed5f7d89af6f90b809e2c0197c6d170 > -- > Regards > > Daniel Danzberger > embeDD GmbH, Alter Postplatz 2, CH-6370 Stans > > _______________________________________________ > Lede-dev mailing list > Lede-dev@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/lede-dev
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