On 11/07/2017 05:36 AM, Nicholas Piggin wrote:
On Mon, 6 Nov 2017 16:16:07 +0100
Florian Weimer <fwei...@redhat.com> wrote:
On 11/06/2017 11:03 AM, Nicholas Piggin wrote:
Florian found a nasty corner case with the VA allocation logic
for crossing from 128TB to 512TB limit on hash, and made a
really superb report of the problem -- traces, reproducer recipes,
analysis, etc. which already mostly solved it.
The first patch in the series should solve Florian's particular
case, the next 3 are other issues with addr_limit. The last
patch is technically a cleanup but I think it's fairly important
in terms of understanding the code and also enabling some BUG
checks (when addr_limit == 0).
I have not tested these exactly on Florian's test case, but
some tests of my own behave better afterwards. Hopefully he has
time to re-test. Some careful review would be welcome too.
I think I have applied the five patches you posted, but I still get a
brk value above 128 TiB:
# /lib64/ld64.so.1 ./a.out
initial brk value: 0x7fffde960000
probing at 0x80000001fffc
I assumed you wanted to reject those?
It was difficult to understand what the intended semantics are, but I
think brk should succeed (it is implemented with MAP_FIXED). Of course
it should not succeed then segfault when you try to access it.
In either case, I recommend to tweak the VM layout, so that ld.so does
not land closely to to the 128 TiB limit, so that the brk failure or
returning of 48-bit addresses is avoided.
Yeah well that's yet another issue. I was not really involved with the
address space extension work. Anees, Kirill, was the intention for the
128T->512T extension logic to be a no-op for all address space allocaiton
except those with explicit addresses?
yes.
-aneesh
