view CONTRIBUTORS @ 28265:332926212ef8

repoview: discard filtered changelog if index isn't shared with unfiltered

Before this patch, revisions rollbacked at failure of previous
transaction might be visible at subsequent operations unintentionally,
if repoview object is reused even after failure of transaction:
e.g. command server and HTTP server are typical cases.

'repoview' uses the tuple of values below of unfiltered changelog as
"the key" to examine validity of filtered changelog cache.

     - length
     - tip node
     - filtered revisions (as hashed value)
     - '_delayed' field

'repoview' compares between "the key" of unfiltered changelog at
previous caching and now, and reuses filtered changelog cache if no
change is detected.

But this comparison indicates only that there is no change between
unfiltered 'repo.changelog' at last caching and now, but not that
filtered changelog cache is valid for current unfiltered one.

'repoview' uses "shallow copy" of unfiltered changelog to create
filtered changelog cache. In this case, 'index' buffer of unfiltered
changelog is also referred by filtered changelog.

At failure of transaction, unfiltered changelog itself is invalidated
(= un-referred) on the 'repo' side (see 0a7610758c42 also). But
'index' of it still contains revisions to be rollbacked at this
failure, and is referred by filtered changelog.

Therefore, even if there is no change between unfiltered
'repo.changelog' at last caching and now, steps below makes rollbacked
revisions visible via filtered changelog unintentionally.

  1. instantiate unfiltered changelog as 'repo.changelog'
     (call it CL1)

  2. make filtered (= shallow copy of) CL1
     (call it FCL1)

  3. cache FCL1 with "the key" of CL1

  4. revisions are appended to 'index', which is shared by CL1 and FCL1

  5. invalidate 'repo.changelog' (= CL1) at failure of transaction

  6. instantiate 'repo.changelog' again at next operation
     (call it CL2)

     CL2 doesn't have revisions added at (4), because it is
     instantiated from '00changelog.i', which isn't changed while
     failed transaction.

  7. compare between "the key" of CL1 and CL2

  8. FCL1 cached at (3) is reused, because comparison at (7) doesn't
     detect change between CL1 at (1) and CL2

  9. revisions rollbacked at (5) are visible via FCL1 unintentionally,
     because FCL1 still refers 'index' changed at (4)

The root cause of this issue is that there is no examination about
validity of filtered changelog cache against current unfiltered one.

This patch discards filtered changelog cache, if its 'index' object
isn't shared with unfiltered one.

BTW, at the time of this patch, redundant truncation of
'00changelog.i' at failure of transaction (see 0a7610758c42 for
detail) often prevents "hg serve" from making already rollbacked
revisions visible, because updating timestamps of '00changelog.i' by
truncation makes "hg serve" discard old repoview object with invalid
filtered changelog cache.

This is reason why this issue is overlooked before this patch, even
though test-bundle2-exchange.t has tests in similar situation: failure
of "hg push" via HTTP by pretxnclose hook on server side doesn't
prevent subsequent commands from looking up outgoing revisions
correctly.

But timestamp on the filesystem doesn't have enough resolution for
recent computation power, and it can't be assumed that this avoidance
always works as expected.

Therefore, without this patch, this issue might appear occasionally.

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>