From: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
To: Michael Haggerty <mhagger@alum.mit.edu>
Cc: Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
Johan Herland <johan@herland.net>,
git@vger.kernel.org
Subject: Re: [PATCH 00/12] Fix some reference-related races
Date: Tue, 18 Jun 2013 19:13:14 +0100 [thread overview]
Message-ID: <51C0A33A.7060802@ramsay1.demon.co.uk> (raw)
In-Reply-To: <51BD5232.20205@alum.mit.edu>
Michael Haggerty wrote:
> Thanks for all of the information.
>
> On 06/15/2013 10:13 PM, Ramsay Jones wrote:
>> Michael Haggerty wrote:
>>> *This patch series must be built on top of mh/reflife.*
[ ... ]
>> You may be wondering why clear_packed_ref_cache() is called? Well, that
>> is because stat_validity_check() *incorrectly* indicates that the
>> packed-refs file has changed. Why does it do that? Well, this is one
>> more example of the problems caused by the cygwin schizophrenic stat()
>> functions. :( [ARGHHHHHHHHH]
>>
[ ... ]
> So if I understand correctly, all of the above is *without* the
> refcounting changes introduced in mh/ref-races? Is so, then it is not
> surprising, as this is exactly the sort of problem that the reference
> counting is meant to solve.
Yes, as I said, this describes the old (non refcounted) series.
This particular problem (the segmentation fault) is fixed by the new
series (as noted below). [Note, however, that the packed-refs file
will still be re-read more often than needed.]
>> Now, turning to the new code, t3211-peel-ref.sh test #7 now works, but
>> test #8 still fails...
[ ... ]
> These "internal error: packed-ref cache cleared while locked" failures
> result from an internal consistency check that clear_packed_ref_cache()
> is not called while the write lock is held on the packed-refs file. A
> call to c_p_r_c() could result from
>
> * a programming error
>
> * a determination based on the packed-refs file stat that the file needs
> to be re-read
>
> Judging from what you said about cygwin, I assume that the latter is
> happening.
Indeed.
> It should be impossible, because the current process is
> holding packed-refs.lock, and therefore other git processes should
> refuse to change the packed-refs file.
:-P You are assuming that a single process can't lie to itself ...
[ ... ]
> Yikes! ECYGWINFAIL.
Ah, NO, this should read ECYGWINGITFAIL.
This is a self-inflicted wound; it has nothing much to do with cygwin.
I should not have assumed that you knew what I meant by "schizophrenic
stat() functions" above; sorry about that! If you are interested, then
the following commits may be useful reading: adbc0b6, 7faee6b, 7974843,
05bab3ea, 924aaf3e and b8a97333.
[ ... ]
>> I haven't checked the remaining test failures to see if they are
>> caused by this code (I don't think so, but ...), but this failure
>> is clearly a cygwin specific issue.
>
> Thanks again for the testing and analysis,
So, unless you feel the need to fix this yourself, you can probably
ignore this issue for now. I will hopefully find time to fix it up
before this topic progresses to next. (Although I don't have any
feeling for the time-frame of this topic).
HTH
ATB,
Ramsay Jones
next prev parent reply other threads:[~2013-06-18 18:40 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-11 21:48 [PATCH 00/12] Fix some reference-related races Michael Haggerty
2013-06-11 21:48 ` [PATCH 01/12] repack_without_ref(): split list curation and entry writing Michael Haggerty
2013-06-12 11:38 ` Jeff King
2013-06-12 11:56 ` Michael Haggerty
2013-06-11 21:48 ` [PATCH 02/12] pack_refs(): split creation of packed refs " Michael Haggerty
2013-06-11 21:48 ` [PATCH 03/12] refs: wrap the packed refs cache in a level of indirection Michael Haggerty
2013-06-11 21:48 ` [PATCH 04/12] refs: implement simple transactions for the packed-refs file Michael Haggerty
2013-06-12 12:01 ` Jeff King
2013-06-11 21:48 ` [PATCH 05/12] refs: manage lifetime of packed refs cache via reference counting Michael Haggerty
2013-06-11 21:48 ` [PATCH 06/12] do_for_each_entry(): increment the packed refs cache refcount Michael Haggerty
2013-06-11 21:48 ` [PATCH 07/12] packed_ref_cache: increment refcount when locked Michael Haggerty
2013-06-11 21:48 ` [PATCH 08/12] Extract a struct stat_data from cache_entry Michael Haggerty
2013-06-11 21:48 ` [PATCH 09/12] add a stat_validity struct Michael Haggerty
2013-06-11 21:48 ` [PATCH 10/12] get_packed_ref_cache: reload packed-refs file when it changes Michael Haggerty
2013-06-11 21:48 ` [PATCH 11/12] for_each_ref: load all loose refs before packed refs Michael Haggerty
2013-06-11 21:48 ` [PATCH 12/12] refs: do not invalidate the packed-refs cache unnecessarily Michael Haggerty
2013-06-12 12:39 ` Jeff King
2013-06-12 12:52 ` [PATCH 00/12] Fix some reference-related races Jeff King
2013-06-15 20:13 ` Ramsay Jones
2013-06-16 5:50 ` Michael Haggerty
2013-06-18 18:13 ` Ramsay Jones [this message]
2013-06-19 5:51 ` Michael Haggerty
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