mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Michael Haggerty <>
To: Jeff King <>
Cc: Git Mailing List <>
Subject: Re: [PATCH] refs: drop "clear packed-refs while locked" assertion
Date: Mon, 1 Jan 2018 16:26:02 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Dec 8, 2017 at 12:22 PM, Jeff King <> wrote:
> This patch fixes a regression in v2.14.0. It's actually fixed already in
> v2.15.0 because all of the packed-ref code there was rewritten. So
> there's no point in applying this on "master" or even "maint". But I
> figured it was worth sharing here in case somebody else runs across it,
> and in case we ever do a v2.14.4 release.

I forgot to respond to this. +1

Reviewed-by: Michael Haggerty <>


> -- >8 --
> In clear_packed_ref_cache(), we assert that we're not
> currently holding the packed-refs lock. But in each of the
> three code paths that can hit this, the assertion is either
> a noop or actively does the wrong thing:
>  1. in rollback_packed_refs(), we will have just released
>     the lock before calling the function, and so the
>     assertion can never trigger.
>  2. get_packed_ref_cache() can reach this assertion via
>     validate_packed_ref_cache(). But it calls the validate
>     function only when it knows that we're not holding the
>     lock, so again, the assertion can never trigger.
>  3. lock_packed_refs() also calls validate_packed_ref_cache().
>     In this case we're _always_ holding the lock, which
>     means any time the validate function has to clear the
>     cache, we'll trigger this assertion and die.
>     This doesn't happen often in practice because the
>     validate function clears the cache only if we find that
>     somebody else has racily rewritten the packed-refs file
>     between the time we read it and the time we took the lock.
>     So most of the time we don't reach the assertion at all
>     (nobody has racily written the file so there's no need
>     to clear the cache). And when we do, it is not actually
>     indicative of a bug; clearing the cache while holding
>     the lock is the right thing to do here.
> This final case is relatively new, being triggerd by the
> extra validation added in fed6ebebf1 (lock_packed_refs():
> fix cache validity check, 2017-06-12).
> Signed-off-by: Jeff King <>
> ---
>  refs/files-backend.c | 2 --
>  1 file changed, 2 deletions(-)
> diff --git a/refs/files-backend.c b/refs/files-backend.c
> index f21a954ce7..dd41e1d382 100644
> --- a/refs/files-backend.c
> +++ b/refs/files-backend.c
> @@ -99,8 +99,6 @@ static void clear_packed_ref_cache(struct files_ref_store *refs)
>         if (refs->packed) {
>                 struct packed_ref_cache *packed_refs = refs->packed;
> -               if (is_lock_file_locked(&refs->packed_refs_lock))
> -                       die("BUG: packed-ref cache cleared while locked");
>                 refs->packed = NULL;
>                 release_packed_ref_cache(packed_refs);
>         }
> --

      reply	other threads:[~2018-01-01 15:33 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-08 11:22 [PATCH] refs: drop "clear packed-refs while locked" assertion Jeff King
2018-01-01 15:26 ` Michael Haggerty [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

  List information:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).