Jeff KingBefore writing the shallow file, we stat() the existing file to make sure it has not been updated since our operation began. However, we do not do so under a lock, so there is a possible race:
1. Process A takes the lock.
2. Process B calls check_shallow_file_for_update and finds
no update.3. Process A commits the lockfile.
4. Process B takes the lock, then overwrite's process A's
changes.We can fix this by doing our check while we hold the lock.
Signed-off-by: Jeff King <peff@peff.net> --- This is a repost of:
http://article.gmane.org/gmane.comp.version-control.git/242795
You picked up the other two related patches as jk/shallow-update-fix, but I suspect this one just got lost in the noise because I didn't format it as a proper series.
shallow.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
Show changes to shallow.c +2 −2
diff --git a/shallow.c b/shallow.c index bbc98b5..75da07a 100644 --- a/shallow.c +++ b/shallow.c @@ -246,9 +246,9 @@ void setup_alternate_shallow(struct lock_file *shallow_lock, struct strbuf sb = STRBUF_INIT; int fd; - check_shallow_file_for_update(); fd = hold_lock_file_for_update(shallow_lock, git_path("shallow"), LOCK_DIE_ON_ERROR); + check_shallow_file_for_update(); if (write_shallow_commits(&sb, 0, extra)) { if (write_in_full(fd, sb.buf, sb.len) != sb.len) die_errno("failed to write to %s", @@ -293,9 +293,9 @@ void prune_shallow(int show_only) strbuf_release(&sb); return; } - check_shallow_file_for_update(); fd = hold_lock_file_for_update(&shallow_lock, git_path("shallow"), LOCK_DIE_ON_ERROR); + check_shallow_file_for_update(); if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) { if (write_in_full(fd, sb.buf, sb.len) != sb.len) die_errno("failed to write to %s",
-- 1.9.0.532.g9ab8f58