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>
This commit is contained in:
Linus Torvalds 2019-10-15 09:56:36 -07:00
parent 02755af0f3
commit 8e0d0ad206

View File

@ -29,7 +29,6 @@ config SPARC
select RTC_DRV_M48T59 select RTC_DRV_M48T59
select RTC_SYSTOHC select RTC_SYSTOHC
select HAVE_ARCH_JUMP_LABEL if SPARC64 select HAVE_ARCH_JUMP_LABEL if SPARC64
select HAVE_FAST_GUP if SPARC64
select GENERIC_IRQ_SHOW select GENERIC_IRQ_SHOW
select ARCH_WANT_IPC_PARSE_VERSION select ARCH_WANT_IPC_PARSE_VERSION
select GENERIC_PCI_IOMAP select GENERIC_PCI_IOMAP