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![John Cai](/assets/img/avatar_default.png)
In the tmp-objdir api, tmp_objdir_create will create a temporary
directory but also register signal handlers responsible for removing
the directory's contents and the directory itself. However, the
function responsible for recursively removing the contents and
directory, remove_dir_recurse() calls opendir(3) and closedir(3).
This can be problematic because these functions allocate and free
memory, which are not async-signal-safe functions. This can lead to
deadlocks.
One place we call tmp_objdir_create() is in git-receive-pack, where
we create a temporary quarantine directory "incoming". Incoming
objects will be written to this directory before they get moved to
the object directory.
We have observed this code leading to a deadlock:
Thread 1 (Thread 0x7f621ba0b200 (LWP 326305)):
#0 __lll_lock_wait_private (futex=futex@entry=0x7f621bbf8b80
<main_arena>) at ./lowlevellock.c:35
#1 0x00007f621baa635b in __GI___libc_malloc
(bytes=bytes@entry=32816) at malloc.c:3064
#2 0x00007f621bae9f49 in __alloc_dir (statp=0x7fff2ea7ed60,
flags=0, close_fd=true, fd=5)
at ../sysdeps/posix/opendir.c:118
#3 opendir_tail (fd=5) at ../sysdeps/posix/opendir.c:69
#4 __opendir (name=<optimized out>)
at ../sysdeps/posix/opendir.c:92
#5 0x0000557c19c77de1 in remove_dir_recurse ()
git#6 0x0000557c19d81a4f in remove_tmp_objdir_on_signal ()
#7 <signal handler called>
git#8 _int_malloc (av=av@entry=0x7f621bbf8b80 <main_arena>,
bytes=bytes@entry=7160) at malloc.c:4116
git#9 0x00007f621baa62c9 in __GI___libc_malloc (bytes=7160)
at malloc.c:3066
git#10 0x00007f621bd1e987 in inflateInit2_ ()
from /opt/gitlab/embedded/lib/libz.so.1
git#11 0x0000557c19dbe5f4 in git_inflate_init ()
git#12 0x0000557c19cee02a in unpack_compressed_entry ()
git#13 0x0000557c19cf08cb in unpack_entry ()
git#14 0x0000557c19cf0f32 in packed_object_info ()
git#15 0x0000557c19cd68cd in do_oid_object_info_extended ()
git#16 0x0000557c19cd6e2b in read_object_file_extended ()
git#17 0x0000557c19cdec2f in parse_object ()
git#18 0x0000557c19c34977 in lookup_commit_reference_gently ()
git#19 0x0000557c19d69309 in mark_uninteresting ()
git#20 0x0000557c19d2d180 in do_for_each_repo_ref_iterator ()
git#21 0x0000557c19d21678 in for_each_ref ()
git#22 0x0000557c19d6a94f in assign_shallow_commits_to_refs ()
git#23 0x0000557c19bc02b2 in cmd_receive_pack ()
git#24 0x0000557c19b29fdd in handle_builtin ()
git#25 0x0000557c19b2a526 in cmd_main ()
git#26 0x0000557c19b28ea2 in main ()
Since we can't do the cleanup in a portable and signal-safe way, skip
the cleanup when we're handling a signal.
This means that when signal handling, the temporary directory may not
get cleaned up properly. This is mitigated by b3cecf49ea
(tmp-objdir: new
API for creating temporary writable databases, 2021-12-06) which changed
the default name and allows gc to clean up these temporary directories.
In the event of a normal exit, we should still be cleaning up via the
atexit() handler.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
317 lines
7 KiB
C
317 lines
7 KiB
C
#include "cache.h"
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#include "tmp-objdir.h"
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#include "chdir-notify.h"
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#include "dir.h"
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#include "sigchain.h"
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#include "string-list.h"
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#include "strbuf.h"
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#include "strvec.h"
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#include "quote.h"
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#include "object-store.h"
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struct tmp_objdir {
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struct strbuf path;
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struct strvec env;
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struct object_directory *prev_odb;
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int will_destroy;
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};
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/*
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* Allow only one tmp_objdir at a time in a running process, which simplifies
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* our atexit cleanup routines. It's doubtful callers will ever need
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* more than one, and we can expand later if so. You can have many such
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* tmp_objdirs simultaneously in many processes, of course.
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*/
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static struct tmp_objdir *the_tmp_objdir;
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static void tmp_objdir_free(struct tmp_objdir *t)
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{
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strbuf_release(&t->path);
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strvec_clear(&t->env);
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free(t);
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}
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int tmp_objdir_destroy(struct tmp_objdir *t)
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{
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int err;
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if (!t)
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return 0;
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if (t == the_tmp_objdir)
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the_tmp_objdir = NULL;
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if (t->prev_odb)
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restore_primary_odb(t->prev_odb, t->path.buf);
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err = remove_dir_recursively(&t->path, 0);
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tmp_objdir_free(t);
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return err;
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}
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static void remove_tmp_objdir(void)
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{
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tmp_objdir_destroy(the_tmp_objdir);
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}
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void tmp_objdir_discard_objects(struct tmp_objdir *t)
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{
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remove_dir_recursively(&t->path, REMOVE_DIR_KEEP_TOPLEVEL);
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}
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/*
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* These env_* functions are for setting up the child environment; the
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* "replace" variant overrides the value of any existing variable with that
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* "key". The "append" variant puts our new value at the end of a list,
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* separated by PATH_SEP (which is what separate values in
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* GIT_ALTERNATE_OBJECT_DIRECTORIES).
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*/
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static void env_append(struct strvec *env, const char *key, const char *val)
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{
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struct strbuf quoted = STRBUF_INIT;
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const char *old;
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/*
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* Avoid quoting if it's not necessary, for maximum compatibility
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* with older parsers which don't understand the quoting.
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*/
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if (*val == '"' || strchr(val, PATH_SEP)) {
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strbuf_addch("ed, '"');
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quote_c_style(val, "ed, NULL, 1);
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strbuf_addch("ed, '"');
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val = quoted.buf;
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}
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old = getenv(key);
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if (!old)
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strvec_pushf(env, "%s=%s", key, val);
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else
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strvec_pushf(env, "%s=%s%c%s", key, old, PATH_SEP, val);
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strbuf_release("ed);
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}
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static void env_replace(struct strvec *env, const char *key, const char *val)
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{
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strvec_pushf(env, "%s=%s", key, val);
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}
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static int setup_tmp_objdir(const char *root)
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{
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char *path;
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int ret = 0;
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path = xstrfmt("%s/pack", root);
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ret = mkdir(path, 0777);
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free(path);
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return ret;
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}
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struct tmp_objdir *tmp_objdir_create(const char *prefix)
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{
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static int installed_handlers;
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struct tmp_objdir *t;
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if (the_tmp_objdir)
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BUG("only one tmp_objdir can be used at a time");
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t = xcalloc(1, sizeof(*t));
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strbuf_init(&t->path, 0);
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strvec_init(&t->env);
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/*
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* Use a string starting with tmp_ so that the builtin/prune.c code
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* can recognize any stale objdirs left behind by a crash and delete
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* them.
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*/
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strbuf_addf(&t->path, "%s/tmp_objdir-%s-XXXXXX", get_object_directory(), prefix);
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if (!mkdtemp(t->path.buf)) {
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/* free, not destroy, as we never touched the filesystem */
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tmp_objdir_free(t);
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return NULL;
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}
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the_tmp_objdir = t;
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if (!installed_handlers) {
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atexit(remove_tmp_objdir);
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installed_handlers++;
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}
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if (setup_tmp_objdir(t->path.buf)) {
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tmp_objdir_destroy(t);
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return NULL;
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}
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env_append(&t->env, ALTERNATE_DB_ENVIRONMENT,
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absolute_path(get_object_directory()));
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env_replace(&t->env, DB_ENVIRONMENT, absolute_path(t->path.buf));
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env_replace(&t->env, GIT_QUARANTINE_ENVIRONMENT,
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absolute_path(t->path.buf));
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return t;
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}
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/*
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* Make sure we copy packfiles and their associated metafiles in the correct
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* order. All of these ends_with checks are slightly expensive to do in
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* the midst of a sorting routine, but in practice it shouldn't matter.
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* We will have a relatively small number of packfiles to order, and loose
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* objects exit early in the first line.
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*/
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static int pack_copy_priority(const char *name)
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{
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if (!starts_with(name, "pack"))
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return 0;
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if (ends_with(name, ".keep"))
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return 1;
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if (ends_with(name, ".pack"))
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return 2;
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if (ends_with(name, ".rev"))
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return 3;
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if (ends_with(name, ".idx"))
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return 4;
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return 5;
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}
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static int pack_copy_cmp(const char *a, const char *b)
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{
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return pack_copy_priority(a) - pack_copy_priority(b);
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}
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static int read_dir_paths(struct string_list *out, const char *path)
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{
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DIR *dh;
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struct dirent *de;
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dh = opendir(path);
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if (!dh)
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return -1;
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while ((de = readdir(dh)))
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if (de->d_name[0] != '.')
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string_list_append(out, de->d_name);
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closedir(dh);
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return 0;
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}
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static int migrate_paths(struct strbuf *src, struct strbuf *dst);
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static int migrate_one(struct strbuf *src, struct strbuf *dst)
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{
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struct stat st;
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if (stat(src->buf, &st) < 0)
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return -1;
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if (S_ISDIR(st.st_mode)) {
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if (!mkdir(dst->buf, 0777)) {
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if (adjust_shared_perm(dst->buf))
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return -1;
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} else if (errno != EEXIST)
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return -1;
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return migrate_paths(src, dst);
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}
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return finalize_object_file(src->buf, dst->buf);
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}
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static int migrate_paths(struct strbuf *src, struct strbuf *dst)
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{
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size_t src_len = src->len, dst_len = dst->len;
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struct string_list paths = STRING_LIST_INIT_DUP;
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int i;
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int ret = 0;
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if (read_dir_paths(&paths, src->buf) < 0)
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return -1;
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paths.cmp = pack_copy_cmp;
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string_list_sort(&paths);
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for (i = 0; i < paths.nr; i++) {
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const char *name = paths.items[i].string;
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strbuf_addf(src, "/%s", name);
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strbuf_addf(dst, "/%s", name);
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ret |= migrate_one(src, dst);
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strbuf_setlen(src, src_len);
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strbuf_setlen(dst, dst_len);
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}
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string_list_clear(&paths, 0);
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return ret;
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}
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int tmp_objdir_migrate(struct tmp_objdir *t)
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{
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struct strbuf src = STRBUF_INIT, dst = STRBUF_INIT;
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int ret;
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if (!t)
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return 0;
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if (t->prev_odb) {
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if (the_repository->objects->odb->will_destroy)
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BUG("migrating an ODB that was marked for destruction");
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restore_primary_odb(t->prev_odb, t->path.buf);
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t->prev_odb = NULL;
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}
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strbuf_addbuf(&src, &t->path);
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strbuf_addstr(&dst, get_object_directory());
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ret = migrate_paths(&src, &dst);
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strbuf_release(&src);
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strbuf_release(&dst);
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tmp_objdir_destroy(t);
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return ret;
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}
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const char **tmp_objdir_env(const struct tmp_objdir *t)
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{
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if (!t)
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return NULL;
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return t->env.v;
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}
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void tmp_objdir_add_as_alternate(const struct tmp_objdir *t)
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{
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add_to_alternates_memory(t->path.buf);
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}
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void tmp_objdir_replace_primary_odb(struct tmp_objdir *t, int will_destroy)
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{
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if (t->prev_odb)
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BUG("the primary object database is already replaced");
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t->prev_odb = set_temporary_primary_odb(t->path.buf, will_destroy);
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t->will_destroy = will_destroy;
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}
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struct tmp_objdir *tmp_objdir_unapply_primary_odb(void)
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{
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if (!the_tmp_objdir || !the_tmp_objdir->prev_odb)
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return NULL;
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restore_primary_odb(the_tmp_objdir->prev_odb, the_tmp_objdir->path.buf);
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the_tmp_objdir->prev_odb = NULL;
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return the_tmp_objdir;
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}
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void tmp_objdir_reapply_primary_odb(struct tmp_objdir *t, const char *old_cwd,
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const char *new_cwd)
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{
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char *path;
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path = reparent_relative_path(old_cwd, new_cwd, t->path.buf);
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strbuf_reset(&t->path);
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strbuf_addstr(&t->path, path);
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free(path);
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tmp_objdir_replace_primary_odb(t, t->will_destroy);
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}
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