On 04/02/2014 06:58 PM, Junio C Hamano wrote: > Jeff King <p...@peff.net> writes: > >> On Tue, Apr 01, 2014 at 05:58:12PM +0200, Michael Haggerty wrote: >> >>> When rolling back the lockfile, call close_lock_file() so that the >>> lock_file's fd field gets set back to -1. This could help prevent >>> confusion in the face of hypothetical future programming errors. >> >> This also solves a race. We could be in the middle of rollback_lock_file >> when we get a signal, and double-close. It's probably not a big deal, >> though, since nobody could have opened a new descriptor in the interim >> that got the same number (so the second close will just fail silently). >> >> Still, this seems like a definite improvement. > > This is probably related to my comments on 2/22, but is "fd" the > only thing that has a non-zero safe value? Perhaps lock_file_init() > that clears the structure fields to 0/NULL and fd to -1, and a > convenience function lock_file_alloc() that does xmalloc() and then > calls lock_file_init() may help us a bit when the lockfile structure > is reused?
The first use of a lock_file object necessarily passes through lock_file(). The only precondition for that function is that the on_list field is zero, which is satisfied by a xcalloc()ed object. Subsequent uses of a lock_file object must *not* zero the object. lock_file objects are added to the lock_file_list and never removed. So zeroing a lock_file object would discard the rest of the linked list. But subsequent uses must also pass through lock_file(), which sees that on_list is set, and assumes that the object is in a self-consistent state as left by commit_lock_file() or rollback_lock_file(). At least that's how it is supposed to work. But lock_file objects are in fact not cleaned up correctly in all circumstances. The next version of this patch series will work to fix that. Michael -- Michael Haggerty mhag...@alum.mit.edu http://softwareswirl.blogspot.com/ -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html