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linux/arch/sparc
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Linus Torvalds 8e0d0ad206 sparc64: disable fast-GUP due to unexplained oopses 
HAVE_FAST_GUP enables the lockless quick page table walker for simple
cases, and is a nice optimization for some random loads that can then
use get_user_pages_fast() rather than the more careful page walker.

However, for some unexplained reason, it seems to be subtly broken on
sparc64.  The breakage is only with some compiler versions and some
hardware, and nobody seems to have figured out what triggers it,
although there's a simple reprodicer for the problem when it does
trigger.

The problem was introduced with the conversion to the generic GUP code
in commit 7b9afb86b6 ("sparc64: use the generic get_user_pages_fast
code"), but nothing looks obviously wrong in that conversion.  It may be
a compiler bug that just hits us with the code reorganization.  Or it
may be something very specific to sparc64.

This disables HAVE_FAST_GUP entirely.  That makes things like futexes a
bit slower, but at least they work.  If we can figure out the trigger,
that would be lovely, but it's been three months already..

Link: https://lore.kernel.org/lkml/20190717215956.GA30369@altlinux.org/
Fixes: 7b9afb86b6 ("sparc64: use the generic get_user_pages_fast code")
Reported-by: Dmitry V Levin <ldv@altlinux.org>
Reported-by: Anatoly Pugachev <matorola@gmail.com>
Requested-by: Meelis Roos <mroos@linux.ee>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-10-15 09:56:36 -07:00
..
boot treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 61 2019-05-24 17:36:45 +02:00
configs sparc: configs: Remove useless UEVENT_HELPER_PATH 2019-06-13 14:12:19 -07:00
crypto crypto: sparc/des - switch to new verification routines 2019-08-22 14:39:37 +10:00
include arch/sparc/include/asm/pgtable_64.h: fix build 2019-09-26 10:27:06 -07:00
kernel ipc: fix sparc64 ipc() wrapper 2019-09-07 21:42:25 +02:00
lib sparc64: Add missing newline at end of file 2019-07-09 14:53:57 -07:00
math-emu treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
mm mm: treewide: clarify pgtable_page_{ctor,dtor}() naming 2019-09-26 10:10:44 -07:00
net sparc: bpf: eliminate zero extension code-gen 2019-05-24 18:58:38 -07:00
oprofile treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
power treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
prom
vdso kbuild: add --hash-style= and --build-id unconditionally 2019-07-17 22:37:51 +09:00
Kbuild treewide: Add SPDX license identifier - Kbuild 2019-05-30 11:32:33 -07:00
Kconfig sparc64: disable fast-GUP due to unexplained oopses 2019-10-15 09:56:36 -07:00
Kconfig.debug Kconfig: consolidate the "Kernel hacking" menu 2018-08-02 08:06:48 +09:00
Makefile sparc: generate uapi header and system call table files 2018-11-18 18:52:22 -08:00