[PATCH v3 18/25] struct lock_file: declare some fields volatile

[Michael Haggerty <mhagger@alum.mit.edu>]

The function remove_lock_file_on_signal() is used as a signal handler.
It is not realistic to make the signal handler conform strictly to the
C standard, which is very restrictive about what a signal handler is
allowed to do.  But let's increase the likelihood that it will work:

The lock_file_list global variable and several fields from struct
lock_file are used by the signal handler.  Declare those values
"volatile" to increase the chance that the signal handler will see a
valid object state.

Suggested-by: Johannes Sixt <j.sixt@viscovery.net>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 cache.h    | 6 +++---
 lockfile.c | 2 +-
 refs.c     | 5 +++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/cache.h b/cache.h
index b7af173..9019c7d 100644
--- a/cache.h
+++ b/cache.h
@@ -538,10 +538,10 @@ extern int refresh_index(struct index_state *, unsigned int flags, const struct
 #define LOCK_SUFFIX_LEN 5
 
 struct lock_file {
-	struct lock_file *next;
+	struct lock_file *volatile next;
 	volatile sig_atomic_t active;
-	int fd;
-	pid_t owner;
+	volatile int fd;
+	volatile pid_t owner;
 	char on_list;
 	char filename[PATH_MAX];
 };
diff --git a/lockfile.c b/lockfile.c
index 50a0541..fce53f1 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -69,7 +69,7 @@
  * See Documentation/api-lockfile.txt for more information.
  */
 
-static struct lock_file *lock_file_list;
+static struct lock_file *volatile lock_file_list;
 static const char *alternate_index_output;
 
 static void remove_lock_file(void)
diff --git a/refs.c b/refs.c
index cb2f825..db8057c 100644
--- a/refs.c
+++ b/refs.c
@@ -2213,15 +2213,16 @@ int commit_packed_refs(void)
 	struct packed_ref_cache *packed_ref_cache =
 		get_packed_ref_cache(&ref_cache);
 	int error = 0;
+	int fd;
 
 	if (!packed_ref_cache->lock)
 		die("internal error: packed-refs not locked");
 	write_or_die(packed_ref_cache->lock->fd,
 		     PACKED_REFS_HEADER, strlen(PACKED_REFS_HEADER));
 
+	fd = packed_ref_cache->lock->fd;
 	do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
-				 0, write_packed_entry_fn,
-				 &packed_ref_cache->lock->fd);
+				 0, write_packed_entry_fn, &fd);
 	if (commit_lock_file(packed_ref_cache->lock))
 		error = -1;
 	packed_ref_cache->lock = NULL;
-- 
1.9.1