On Mon, Dec 30, 2024 at 11:38:53PM +1100, Mark Jamsek wrote:
> This got lost on IRC the other day when I should have sent it to the
> list: stsp reported that the tog test_log_mark_keymap regression test
> would randomly hang, which I was able to reproduce.
> 
> This is due to a race condition between the main thread checking the
> log_complete flag and the log thread setting it. When the F keymap is
> entered to toggle fullscreen, the main thread might need more commits
> queued to fully populate the log view when redrawing the screen. So it
> first checks the log_complete flag to see if the commit graph has
> already been traversed and, if so, doesn't bother waking the log thread
> to request any more commits. But if the log_complete flag isn't set, it
> does wake the log thread and than waits for it to signal when a commit
> is loaded.
> 
> In the log thread, after we have finished traversing the commit graph,
> we briefly release the mutex before setting the log_complete flag and
> this causes the race: the main thread checks and the flag is unset so
> it wakes the log thread and then waits on the log thread in
> trigger_log_thread() to signal when a new commit is loaded.
> In between the main thread checking the flag, the log thread exits
> the loop and sets the flag.
> 
> The fix sets the flag in the loop before releasing the mutex.
> And because we can exit the loop on error or receipt of a fatal signal,
> we also keep the existing log_complete assignment outside the loop.

ok, thanks for tracking this down!