Fix index preloading for racy dirty case
- From
Linus Torvalds <torvalds@linux-foundation.org>
- Date
- Nov 17, 2008, 17:01 UTC
- Message-ID
- <alpine.LFD.2.00.0811170850170.3468@nehalem.linux-foundation.org>
- In-Reply-To
- <alpine.LFD.2.00.0811170846390.3468@nehalem.linux-foundation.org>
In the threaded index preloading case, we must be sure to always use the CE_MATCH_RACY_IS_DIRTY flag when calling ie_match_stat(), in order to make sure that we only ever look at the stat() data, and don't try to do anything fancy.
Because most of git internals are not thread-safe, and must not be called in parallel.
Otherwise, what happens is that if the timestamps indicate that an entry _might_ be dirty, we might start actually comparing filesystem data with the object database. And we mustn't do that, because that would involve looking up and creating the object structure, and that whole code sequence with read_sha1_file() where we look up and add objects to the hashes is definitely not thread-safe.
Nor do we want to add locking, because the whole point of the preload was to be simple and not affect anything else. With CE_MATCH_RACY_IS_DIRTY, we get what we wanted, and we'll just leave the hard cases well alone, to be done later in the much simpler serial case.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> ---
On Mon, 17 Nov 2008, Linus Torvalds wrote:
> > Oh, damn. I had forgotten that check_fs() doesn't just do a "lstat()" any > more. You're right.
Never mind the "any more". I don't think it ever did.
But I do think that this is trivially fixed, and I should have thought about it. And while I didn't reproduce your SIGSEGV, I think this trivial patch should fix it.
Sorry about the mindfart.
preload-index.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/preload-index.c b/preload-index.c index 3ce42e0..a6a6bdb 100644 --- a/preload-index.c +++ b/preload-index.c @@ -43,7 +43,7 @@ static void *preload_thread(void *_data) continue; if (lstat(ce->name, &st)) continue; - if (ie_match_stat(index, ce, &st, 0)) + if (ie_match_stat(index, ce, &st, CE_MATCH_RACY_IS_DIRTY)) continue; ce_mark_uptodate(ce); } while (--nr > 0);