From 9dd330e6cad6ce11557acb18f35136c549d8ac1b Mon Sep 17 00:00:00 2001 From: Jeff King Date: Tue, 1 Sep 2015 18:14:09 -0400 Subject: rerere: release lockfile in non-writing functions There's a bug in builtin/am.c in which we take a lock on MERGE_RR recursively. But rather than fix am.c, this patch fixes the confusing interface from rerere.c that caused the bug. Read on for the gory details. The setup_rerere() function both reads the existing MERGE_RR file, and takes MERGE_RR.lock. In the rerere() and rerere_forget() functions, we end up in write_rr(), which will then commit the lock file. But for functions like rerere_clear() that do not write to MERGE_RR, we expect the caller to have handled setup_rerere(). That caller would then need to release the lockfile, but it can't; the lock struct is local to rerere.c. For builtin/rerere.c, this is OK. We run a single rerere operation and then exit immediately, which has the side effect of rolling back the lockfile. But in builtin/am.c, this is actively wrong. If we run "git am -3 --skip", we call setup-rerere twice without releasing the lock: 1. The "--skip" causes us to call am_rerere_clear(), which calls setup_rerere(), but never drops the lock. 2. We then proceed to the next patch. 3. The "--3way" may cause us to call rerere() to handle conflicts in that patch, but we are already holding the lock. The lockfile code dies with: BUG: prepare_tempfile_object called for active object We could fix this by having rerere_clear() call rollback_lock_file(). But it feels a bit odd for it to roll back a lockfile that it did not itself take. So let's simplify the interface further, and handle setup_rerere in the function itself, taking away the question from the caller over whether they need to do so. We can give rerere_gc() the same treatment, as well (even though it doesn't have any callers besides builtin/rerere.c at this point). Note that these functions don't take flags from their callers to pass along to setup_rerere; that's OK, because the flags would not be meaningful for what they are doing. Both of those functions need to hold the lock because even though they do not write to MERGE_RR, they are still writing and should be protected from a simultaneous "rerere" run. But rerere_remaining(), "rerere diff", and "rerere status" are all read-only operations. They want to setup_rerere(), but do not care about taking the lock in the first place. Since our update of MERGE_RR is the usual atomic rename done by commit_lock_file, they can just do a lockless read. For that, we teach setup_rerere a READONLY flag to avoid the lock. As a bonus, this pushes builtin/rerere.c's setup_rerere call closer to the functions that use it. Which means that "git rerere totally-bogus-command" will no longer silently exit(0) in a repository without rerere enabled. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- builtin/am.c | 5 ----- builtin/rerere.c | 18 +++++++++--------- 2 files changed, 9 insertions(+), 14 deletions(-) (limited to 'builtin') diff --git a/builtin/am.c b/builtin/am.c index 27165a6730..83b3d86e67 100644 --- a/builtin/am.c +++ b/builtin/am.c @@ -2057,11 +2057,6 @@ static int clean_index(const unsigned char *head, const unsigned char *remote) static void am_rerere_clear(void) { struct string_list merge_rr = STRING_LIST_INIT_DUP; - int fd = setup_rerere(&merge_rr, 0); - - if (fd < 0) - return; - rerere_clear(&merge_rr); string_list_clear(&merge_rr, 1); } diff --git a/builtin/rerere.c b/builtin/rerere.c index 7afadd2ead..12535c9b4f 100644 --- a/builtin/rerere.c +++ b/builtin/rerere.c @@ -50,7 +50,7 @@ static int diff_two(const char *file1, const char *label1, int cmd_rerere(int argc, const char **argv, const char *prefix) { struct string_list merge_rr = STRING_LIST_INIT_DUP; - int i, fd, autoupdate = -1, flags = 0; + int i, autoupdate = -1, flags = 0; struct option options[] = { OPT_SET_INT(0, "rerere-autoupdate", &autoupdate, @@ -79,18 +79,16 @@ int cmd_rerere(int argc, const char **argv, const char *prefix) return rerere_forget(&pathspec); } - fd = setup_rerere(&merge_rr, flags); - if (fd < 0) - return 0; - if (!strcmp(argv[0], "clear")) { rerere_clear(&merge_rr); } else if (!strcmp(argv[0], "gc")) rerere_gc(&merge_rr); - else if (!strcmp(argv[0], "status")) + else if (!strcmp(argv[0], "status")) { + if (setup_rerere(&merge_rr, flags | RERERE_READONLY) < 0) + return 0; for (i = 0; i < merge_rr.nr; i++) printf("%s\n", merge_rr.items[i].string); - else if (!strcmp(argv[0], "remaining")) { + } else if (!strcmp(argv[0], "remaining")) { rerere_remaining(&merge_rr); for (i = 0; i < merge_rr.nr; i++) { if (merge_rr.items[i].util != RERERE_RESOLVED) @@ -100,13 +98,15 @@ int cmd_rerere(int argc, const char **argv, const char *prefix) * string_list_clear() */ merge_rr.items[i].util = NULL; } - } else if (!strcmp(argv[0], "diff")) + } else if (!strcmp(argv[0], "diff")) { + if (setup_rerere(&merge_rr, flags | RERERE_READONLY) < 0) + return 0; for (i = 0; i < merge_rr.nr; i++) { const char *path = merge_rr.items[i].string; const char *name = (const char *)merge_rr.items[i].util; diff_two(rerere_path(name, "preimage"), path, path, path); } - else + } else usage_with_options(rerere_usage, options); string_list_clear(&merge_rr, 1); -- cgit v1.2.3