Re: [PATCH] tools/libxl: Fixes to stream v2 task joining logic

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 23/07/15 12:38, Wei Liu wrote:
> On Thu, Jul 23, 2015 at 12:09:38PM +0100, Andrew Cooper wrote:
>> During review of the libxl migration v2 series, I changes the task
>> joining logic, but clearly didn't think the result through
>> properly. This patch fixes several errors.
>>
>> 1) Do not call check_all_finished() in the success cases of
>> libxl__xc_domain_{save,restore}_done().  It serves no specific purpose
>> as the save helper state will report itself as inactive by this point,
>> and avoids triggering a second stream->completion_callback() in the case
>> that write_toolstack_record()/stream_continue() record errors
>> synchronously themselves.
>>
>> 2) Only ever set stream->rc in stream_complete().  The first version of
>> the migration v2 series had separate rc and joined_rc parameters, where
>> this logic worked.  However when combining the two, the teardown path
>> fails to trigger if stream_done() records stream->rc itself.  A side
>> effect of this is that stream_done() needs to take an rc parameter.
>>
>> 3) Avoid stacking of check_all_finished() via synchronous teardown of
>> tasks.  If the _abort() functions call back synchronously,
>> stream->completion_callback() ends up getting called twice, as first and
>> last check_all_finished() frames observe each task being finished.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> CC: Ian Campbell <Ian.Campbell@citrix.com>
>> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
>> CC: Wei Liu <wei.liu2@citrix.com>
>>
>> ---
>> I found this while working to fix the toolstack record issue, but am
>> posting this bugfix ahead of the other work as OSSTest has tripped over
>> the issue.
> This change itself doesn't seem to have anything to do with libxc. In
> OSSTest the error that triggers this knock on effect is the failure of
> xc_map_foreign_bulk. Does that mean this patch only fix half of the
> problem seen in OSSTest?

Saving to image new xl format (info 0x3/0x0/1797)
xc: info: In experimental xc_domain_save2
xc: info: Saving domain 2, type x86 HVM
xc: progress: Memory: 67584/1344513    5%
xc: progress: Memory: 135168/1344513   10%
xc: progress: Memory: 201728/1344513   15%
xc: progress: Memory: 269312/1344513   20%
xc: progress: Memory: 336896/1344513   25%
xc: progress: Memory: 403456/1344513   30%
xc: progress: Memory: 471040/1344513   35%
xc: progress: Memory: 538624/1344513   40%
xc: progress: Memory: 605184/1344513   45%
xc: progress: Memory: 672768/1344513   50%
xc: progress: Memory: 740352/1344513   55%
xc: error: xc_map_foreign_bulk: mmap failed (12 = Cannot allocate
memory): Internal error
xc: error: Failed to map guest pages (12 = Cannot allocate memory):
Internal error
xc: error: Save failed (12 = Cannot allocate memory): Internal error
libxl: error: libxl_stream_write.c:267:libxl__xc_domain_save_done:
saving domain: domain responded to suspend request: Cannot allocate memory
xl: libxl_event.c:1866: libxl__ao_inprogress_gc: Assertion
`!ao->complete' failed.


I don't know why xc_map_foreign_bulk() failed, but at a guess I would
day dom0 is out of RAM.

This patch fixes the libxl assertion.

~Andrew