mmap failure [was: cygrunsrv + sshd + rsync = 20 times too slow -- throttled?]

[Corinna Vinschen]

On Sep  6 13:38, Ken Brown via Cygwin wrote:
> On 9/6/2021 1:12 PM, Ken Brown via Cygwin wrote:
> > On 9/6/2021 11:32 AM, Corinna Vinschen via Cygwin wrote:
> > > On Sep  5 09:24, Ken Brown via Cygwin wrote:
> > > > On 9/4/2021 8:04 PM, Ken Brown via Cygwin wrote:
> > > > > On 9/4/2021 6:58 PM, Ken Brown via Cygwin wrote:
> > > > > > Here are the correct commits:
> > > > > > 
> > > > > > 8169e39ab Cygwin: C++17: register keyword is deprecated
> > > > > > 3ca80b360 Cygwin: dumper: fix up GCC pragma for g++ 11.2
> > > > > > bdb7991db Cygwin: workaround a g++ 11.2 initialization bug
> > > > > > 801120c1f Cygwin: loader script: add DWARF 5 sections
> > > > > > d5cc66426 Cygwin: testsuite: avoid "conflicting types" gcc warning
> > > > > > c2fe205b5 strstr: avoid warnings
> > > > > > 76c2c7a89 ldexp/ldexpf: avoid assembler warning
> > > > > > eeeb5650c Cygwin: fix declaration of RtlInitEmptyUnicodeString
> > > > > > 
> > > > > > > 
> > > > > > > > So there appears to be something wrong with cygwin1.dll
> > > > > > > > built with the current build tools (gcc 11.2.0, binutils
> > > > > > > > 2.37, not sure what else is relevant).
> > > > > 
> > > > > Wait a minute...I'll bet this is related to the MEM_EXTENDED_PARAMETER
> > > > > initialization problem that was dealt with in commit bdb7991db.
> > > > 
> > > > More data: When I run the test case under gdb, it succeeds.  When I run it
> > > > under strace, I see VirtualAlloc2 in fhandler_dev_zero::mmap failing with
> > > > windows error 87.
> > > 
> > > Are the const's I added to the MEM_EXTENDED_PARAMETER data invalid,
> > > perhaps?
> > 
> > I tried removing them, and I got the same error.  I also tried removing
> > static, and I tried removing both static and const.
> 
> BTW, when I reported that the test case succeeds under gdb, that only
> happens when I build the test case without optimization.  If I build with
> -O2, it fails under gdb also.  [In all my tests, I built cygwin1.dll without
> optimization.] This makes no sense to me at all.

Good hint.  I found the culprit.  With optimization, the code doesn't
set the "Reserved" bits in the first struct of MEM_EXTENDED_PARAMETER
to 0.  This is at least required by the VirtualAlloc2 function, though.
Needless to say that this behaviour isn't documented...

I'll push a patch shortly.


Thanks,
Corinna