Re: unexpected auto-maintenance, was Re: git hogs the CPU, RAM and storage despite its config

> On Sat, May 09, 2026 at 01:52:49PM -0400, Jeff King wrote:
>> I don't think this affected the old "git gc --detach" because it takes
>> the lock after daemonizing[1]. We can't do the same here, though, since we
>> need to hold the lock for the foreground tasks. So either we need to
>> release and re-take the lock between foreground and background tasks, or
>> we need to teach the daemonize() function to update the "owner" field on
>> all of the tempfiles to the new child[2].
> 
> I agree. We can't simply do what was done in 329e6e8794c (gc: save log
> from daemonized gc --auto and print it next time, 2015-09-19), for
> exactly the reason that you stated.
> 
> Dropping and re-acquiring the lock is possible, but it's racy since
> there is a gap during the critical window while we fork(). I believe
> that the only airtight way to do this is to update the owner field of
> the tempfiles we want to pass down during daemonization.

> (As an aside, do we want to do that for all tempfiles? It might be nice
> to have a "->reassign_on_fork" flag or something on the tempfile struct
> in case there are instances where the parent wants to retain ownership
> of the tempfile after fork()-ing, but I can't think of any off the top
> of my head. If we do introduce such a field, it should probably default
> to "true" to avoid any foot-guns.)
> 
>> Ultimately fixing the lock bug will solve that. Though if doing so is
>> too complicated for a quick maint release, I'm tempted to say we should
>> consider reverting 452b12c2e0 for a potential v2.54.1 (as there were a
>> few other regression fixes so far, I assume we'll have one soon-ish).
> 
> I think something like the following (untested) would do the trick:
> 
> --- 8< ---
> diff --git a/setup.c b/setup.c
> index 7ec4427368a..c07aeac4f7d 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -22,6 +22,7 @@
>   #include "chdir-notify.h"
>   #include "path.h"
>   #include "quote.h"
> +#include "tempfile.h"
>   #include "trace.h"
>   #include "trace2.h"
>   #include "worktree.h"
> @@ -2162,12 +2163,17 @@ int daemonize(void)
>   	errno = ENOSYS;
>   	return -1;
>   #else
> -	switch (fork()) {
> +	pid_t ppid = getpid();
> +	pid_t pid;
> +
> +	switch ((pid = fork())) {
>   		case 0:
> +			reassign_tempfile_ownership(ppid, getpid());
>   			break;
>   		case -1:
>   			die_errno(_("fork failed"));
>   		default:
> +			reassign_tempfile_ownership(ppid, pid);
>   			exit(0);
>   	}
>   	if (setsid() == -1)
> diff --git a/tempfile.c b/tempfile.c
> index 82dfa3d82f2..f0fdf582794 100644
> --- a/tempfile.c
> +++ b/tempfile.c
> @@ -373,3 +373,15 @@ int delete_tempfile(struct tempfile **tempfile_p)
> 
>   	return err ? -1 : 0;
>   }
> +
> +void reassign_tempfile_ownership(pid_t from, pid_t to)
> +{
> +	volatile struct volatile_list_head *pos;
> +
> +	list_for_each(pos, &tempfile_list) {
> +		struct tempfile *p = list_entry(pos, struct tempfile, list);
> +
> +		if (is_tempfile_active(p) && p->owner == from)
> +			p->owner = to;
> +	}
> +}