powerpc hugepage leak caused by 576ed913 "block: use bio_add_page in bio_iov_iter_get_pages"

[David Gibson]

On Thu, Apr 25, 2019 at 08:19:58AM +0200, Christoph Hellwig wrote:
> Just curious:  What exact trees do you see this with?  This area
> changed a lot with the multipage bvec support, and subsequent fixes.

So, I tried it with 576ed913 itself and with 576ed913^ to verify that
it didn't happen there.  The problem also occurred with Linus' tree as
of when I started bisecting, which appears to have been 444fe991.
Actually, come to that, here's the whole bisect log in case it's
helpful:

# git bisect log
git bisect start
# good: [bebc6082da0a9f5d47a1ea2edc099bf671058bd4] Linux 4.14
git bisect good bebc6082da0a9f5d47a1ea2edc099bf671058bd4
# bad: [444fe991353987c1c9bc5ab1f903d01f1b4ad415] Merge tag 'riscv-for-linus-5.1-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/palmer/riscv-linux
git bisect bad 444fe991353987c1c9bc5ab1f903d01f1b4ad415
# good: [399c4129eba6145924ab90363352b7bdcd554751] Merge tag 'pxa-for-4.19-dma_slave_map' of https://github.com/rjarzmik/linux
git bisect good 399c4129eba6145924ab90363352b7bdcd554751
# bad: [73b6f96cbc0162787bcbdac5f538167084c8d605] Merge branch 'drm-fixes-4.20' of git://people.freedesktop.org/~agd5f/linux into drm-fixes
git bisect bad 73b6f96cbc0162787bcbdac5f538167084c8d605
# good: [85a585918fb4122ad26b6febaec5c3c90bf2535c] Merge tag 'loadpin-security-next' of https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux into next-loadpin
git bisect good 85a585918fb4122ad26b6febaec5c3c90bf2535c
# bad: [3acbd2de6bc3af215c6ed7732dfc097d1e238503] Merge tag 'sound-4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect bad 3acbd2de6bc3af215c6ed7732dfc097d1e238503
# good: [8f18da47211554f1ef674fef627c05f23b75a8e0] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next
git bisect good 8f18da47211554f1ef674fef627c05f23b75a8e0
# bad: [0d1b82cd8ac2e8856ae9045c97782ac1c359929c] Merge branch 'ras-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect bad 0d1b82cd8ac2e8856ae9045c97782ac1c359929c
# bad: [1650ac53066577a5e83fe3e9d992c9311597ff8c] Merge tag 'mmc-v4.20' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc
git bisect bad 1650ac53066577a5e83fe3e9d992c9311597ff8c
# bad: [6ab9e09238fdfd742fe23b81e2d385a1cab49d9b] Merge tag 'for-4.20/block-20181021' of git://git.kernel.dk/linux-block
git bisect bad 6ab9e09238fdfd742fe23b81e2d385a1cab49d9b
# good: [528985117126f11beea339cf39120ee99da04cd2] Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
git bisect good 528985117126f11beea339cf39120ee99da04cd2
# bad: [2cf99bbd106f89fc72f778e8ad9d5538f1ef939b] lightnvm: pblk: add helpers for chunk addresses
git bisect bad 2cf99bbd106f89fc72f778e8ad9d5538f1ef939b
# bad: [33b14f67a4e1eabd219fd6543da8f15ed86b641c] nvme: register ns_id attributes as default sysfs groups
git bisect bad 33b14f67a4e1eabd219fd6543da8f15ed86b641c
# bad: [27ca1d4ed04ea29dc77b47190a3cc82697023e76] block: move req_gap_back_merge to blk.h
git bisect bad 27ca1d4ed04ea29dc77b47190a3cc82697023e76
# bad: [07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60] blkcg: convert blkg_lookup_create to find closest blkg
git bisect bad 07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60
# good: [cbeb869a3d1110450186b738199963c5e68c2a71] block, bfq: correctly charge and reset entity service in all cases
git bisect good cbeb869a3d1110450186b738199963c5e68c2a71
# bad: [576ed9135489c723fb39b97c4e2c73428d06dd78] block: use bio_add_page in bio_iov_iter_get_pages
git bisect bad 576ed9135489c723fb39b97c4e2c73428d06dd78
# good: [c8765de0adfcaaf4ffb2d951e07444f00ffa9453] blok, bfq: do not plug I/O if all queues are weight-raised
git bisect good c8765de0adfcaaf4ffb2d951e07444f00ffa9453
# first bad commit: [576ed9135489c723fb39b97c4e2c73428d06dd78] block: use bio_add_page in bio_iov_iter_get_pages

The problem also occurred with the RHEL8 downstream kernel tree.
That's based on 4.18, but has 576ed913 backported.

> So I'd be really curious if it can be reproduced with Jens' latest
> block for-5.2 tree (which should be in latest linux-next).

I'll see if I can try that when I next get access to the machine.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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