Re: [linux-4.1 test] 79008: regressions - FAIL

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2016-02-02 at 14:10 +0000, Ian Campbell wrote:
> 
> When running Jessie userspace the issue only appeared somewhere between
> Linux v3.18 and v3.19, I'm currently looking at bisecting that range in
> case the commit which exposed the issue gives a hint (I fear it wont
> though).

Bisecting the dom0 failure lead me to:

3567258d281b5b515d5165ed23851d9f84087e7d is the first bad commit
commit 3567258d281b5b515d5165ed23851d9f84087e7d
Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Date:   Fri Nov 21 11:05:39 2014 +0000

    xen/arm: use hypercall to flush caches in map_page
    
    In xen_dma_map_page, if the page is a local page, call the native
    map_page dma_ops. If the page is foreign, call __xen_dma_map_page that
    issues any required cache maintenane operations via hypercall.
    
    The reason for doing this is that the native dma_ops map_page could
    allocate buffers than need to be freed. If the page is foreign we don't
    call the native unmap_page dma_ops function, resulting in a memory leak.
    
    Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

However AIUI this commit is supposed to be a NOP for all dom0 initiated
I/O, which is all which should be occurring in a test which only involves
ssh to dom0.

Something to do with cache flushes, dma and/or barriers does seem like a
plausible candidate for there error though.

Ian.

NB last few were combined with 
    git cherry-pick --no-commit 28603d13997e2ef47f18589cc9a44553aad49c86
else the NIC driver just crashes on boot.

git bisect start
# bad: [bfa76d49576599a4b9f9b7a71f23d73d6dcff735] Linux 3.19
git bisect bad bfa76d49576599a4b9f9b7a71f23d73d6dcff735
# good: [b2776bf7149bddd1f4161f14f79520f17fc1d71d] Linux 3.18
git bisect good b2776bf7149bddd1f4161f14f79520f17fc1d71d
# bad: [54850e73e86e3bc092680d1bdb84eb322f982ab1] zram: change parameter from vaild_io_request()
git bisect bad 54850e73e86e3bc092680d1bdb84eb322f982ab1
# good: [6b9e2cea428cf7af93a84bcb865e478d8bf1c165] Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost
git bisect good 6b9e2cea428cf7af93a84bcb865e478d8bf1c165
# good: [b5f185f33d0432cef6ff78765e033dfa8f4de068] Merge tag 'master-2014-12-08' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next
git bisect good b5f185f33d0432cef6ff78765e033dfa8f4de068
# good: [bae41e45b7400496b9bf0c70c6004419d9987819] Merge tag 'sound-3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect good bae41e45b7400496b9bf0c70c6004419d9987819
# good: [c0222ac086669a631814bbf857f8c8023452a4d7] Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus
git bisect good c0222ac086669a631814bbf857f8c8023452a4d7
# bad: [a7cb7bb664543e4562ab0e9a072470d2d18c761f] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial
git bisect bad a7cb7bb664543e4562ab0e9a072470d2d18c761f
# bad: [9bfccec24e31f4f83445cfe0c1b0a5ef97900628] Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
git bisect bad 9bfccec24e31f4f83445cfe0c1b0a5ef97900628
# bad: [4e8790f77f051d4cc745a57b48a73052521e8dfc] Merge branch 'for-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata
git bisect bad 4e8790f77f051d4cc745a57b48a73052521e8dfc
# skip: [b1df4a56bf4a61113e8928f932d346bed6eef553] xen/pciback: Restore configuration space when detaching from a guest.
git bisect skip b1df4a56bf4a61113e8928f932d346bed6eef553
# bad: [9d050966e2eb37a643ac15904b6a8fda7fcfabe9] Merge tag 'stable/for-linus-3.19-rc0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip
git bisect bad 9d050966e2eb37a643ac15904b6a8fda7fcfabe9
# bad: [9490c6c67e2f41760de8ece4e4f56f75f84ceb9e] swiotlb-xen: call xen_dma_sync_single_for_device when appropriate
git bisect bad 9490c6c67e2f41760de8ece4e4f56f75f84ceb9e
# good: [a0f2dee0cd651efb5fac6a1d35b0a14460ebcdd4] xen: add a dma_addr_t dev_addr argument to xen_dma_map_page
git bisect good a0f2dee0cd651efb5fac6a1d35b0a14460ebcdd4
# bad: [a4dba130891271084344c12537731542ec77cb85] xen/arm/arm64: introduce xen_arch_need_swiotlb
git bisect bad a4dba130891271084344c12537731542ec77cb85
# bad: [3567258d281b5b515d5165ed23851d9f84087e7d] xen/arm: use hypercall to flush caches in map_page
git bisect bad 3567258d281b5b515d5165ed23851d9f84087e7d
# first bad commit: [3567258d281b5b515d5165ed23851d9f84087e7d] xen/arm: use hypercall to flush caches in map_page

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