From dbdcab6b89ea86fe58ece01bbb7be297ff23b2c4 Mon Sep 17 00:00:00 2001 From: Paulo Casaretto Date: Thu, 22 Jan 2026 19:23:35 +0000 Subject: lockfile: add PID file for debugging stale locks When a lock file is held, it can be helpful to know which process owns it, especially when debugging stale locks left behind by crashed processes. Add an optional feature that creates a companion PID file alongside each lock file, containing the PID of the lock holder. For a lock file "foo.lock", the PID file is named "foo~pid.lock". The tilde character is forbidden in refnames and allowed in Windows filenames, which guarantees no collision with the refs namespace (e.g., refs "foo" and "foo~pid" cannot both exist). The file contains a single line in the format "pid " followed by a newline. The PID file is created when a lock is acquired (if enabled), and automatically cleaned up when the lock is released (via commit or rollback). The file is registered as a tempfile so it gets cleaned up by signal and atexit handlers if the process terminates abnormally. When a lock conflict occurs, the code checks for an existing PID file and, if found, uses kill(pid, 0) to determine if the process is still running. This allows providing context-aware error messages: Lock is held by process 12345. Wait for it to finish, or remove the lock file to continue. Or for a stale lock: Lock was held by process 12345, which is no longer running. Remove the stale lock file to continue. The feature is controlled via core.lockfilePid configuration (boolean). Defaults to false. When enabled, PID files are created for all lock operations. Existing PID files are always read when displaying lock errors, regardless of the core.lockfilePid setting. This ensures helpful diagnostics even when the feature was previously enabled and later disabled. Signed-off-by: Paulo Casaretto Signed-off-by: Junio C Hamano --- lockfile.c | 168 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 154 insertions(+), 14 deletions(-) (limited to 'lockfile.c') diff --git a/lockfile.c b/lockfile.c index 1d5ed01682..13e2ad1307 100644 --- a/lockfile.c +++ b/lockfile.c @@ -6,6 +6,9 @@ #include "abspath.h" #include "gettext.h" #include "lockfile.h" +#include "parse.h" +#include "strbuf.h" +#include "wrapper.h" /* * path = absolute or relative path name @@ -71,19 +74,115 @@ static void resolve_symlink(struct strbuf *path) strbuf_reset(&link); } +/* + * Lock PID file functions - write PID to a foo~pid.lock file alongside + * the lock file for debugging stale locks. The PID file is registered + * as a tempfile so it gets cleaned up by signal/atexit handlers. + * + * Naming: For "foo.lock", the PID file is "foo~pid.lock". The tilde is + * forbidden in refnames and allowed in Windows filenames, guaranteeing + * no collision with the refs namespace. + */ + +/* Global config variable, initialized from core.lockfilePid */ +int lockfile_pid_enabled; + +/* + * Path generation helpers. + * Given base path "foo", generate: + * - lock path: "foo.lock" + * - pid path: "foo-pid.lock" + */ +static void get_lock_path(struct strbuf *out, const char *path) +{ + strbuf_addstr(out, path); + strbuf_addstr(out, LOCK_SUFFIX); +} + +static void get_pid_path(struct strbuf *out, const char *path) +{ + strbuf_addstr(out, path); + strbuf_addstr(out, LOCK_PID_INFIX); + strbuf_addstr(out, LOCK_SUFFIX); +} + +static struct tempfile *create_lock_pid_file(const char *pid_path, int mode) +{ + struct strbuf content = STRBUF_INIT; + struct tempfile *pid_tempfile = NULL; + int fd; + + if (!lockfile_pid_enabled) + goto out; + + fd = open(pid_path, O_WRONLY | O_CREAT | O_EXCL, mode); + if (fd < 0) + goto out; + + strbuf_addf(&content, "pid %" PRIuMAX "\n", (uintmax_t)getpid()); + if (write_in_full(fd, content.buf, content.len) < 0) { + warning_errno(_("could not write lock pid file '%s'"), pid_path); + close(fd); + unlink(pid_path); + goto out; + } + + close(fd); + pid_tempfile = register_tempfile(pid_path); + +out: + strbuf_release(&content); + return pid_tempfile; +} + +static int read_lock_pid(const char *pid_path, uintmax_t *pid_out) +{ + struct strbuf content = STRBUF_INIT; + const char *val; + int ret = -1; + + if (strbuf_read_file(&content, pid_path, LOCK_PID_MAXLEN) <= 0) + goto out; + + strbuf_rtrim(&content); + + if (skip_prefix(content.buf, "pid ", &val)) { + char *endptr; + *pid_out = strtoumax(val, &endptr, 10); + if (*pid_out > 0 && !*endptr) + ret = 0; + } + + if (ret) + warning(_("malformed lock pid file '%s'"), pid_path); + +out: + strbuf_release(&content); + return ret; +} + /* Make sure errno contains a meaningful value on error */ static int lock_file(struct lock_file *lk, const char *path, int flags, int mode) { - struct strbuf filename = STRBUF_INIT; + struct strbuf base_path = STRBUF_INIT; + struct strbuf lock_path = STRBUF_INIT; + struct strbuf pid_path = STRBUF_INIT; - strbuf_addstr(&filename, path); + strbuf_addstr(&base_path, path); if (!(flags & LOCK_NO_DEREF)) - resolve_symlink(&filename); + resolve_symlink(&base_path); + + get_lock_path(&lock_path, base_path.buf); + get_pid_path(&pid_path, base_path.buf); + + lk->tempfile = create_tempfile_mode(lock_path.buf, mode); + if (lk->tempfile) + lk->pid_tempfile = create_lock_pid_file(pid_path.buf, mode); - strbuf_addstr(&filename, LOCK_SUFFIX); - lk->tempfile = create_tempfile_mode(filename.buf, mode); - strbuf_release(&filename); + strbuf_release(&base_path); + strbuf_release(&lock_path); + strbuf_release(&pid_path); return lk->tempfile ? lk->tempfile->fd : -1; } @@ -151,16 +250,49 @@ static int lock_file_timeout(struct lock_file *lk, const char *path, void unable_to_lock_message(const char *path, int err, struct strbuf *buf) { if (err == EEXIST) { - strbuf_addf(buf, _("Unable to create '%s.lock': %s.\n\n" - "Another git process seems to be running in this repository, e.g.\n" - "an editor opened by 'git commit'. Please make sure all processes\n" - "are terminated then try again. If it still fails, a git process\n" - "may have crashed in this repository earlier:\n" - "remove the file manually to continue."), - absolute_path(path), strerror(err)); - } else + const char *abs_path = absolute_path(path); + struct strbuf lock_path = STRBUF_INIT; + struct strbuf pid_path = STRBUF_INIT; + uintmax_t pid; + int pid_status = 0; /* 0 = unknown, 1 = running, -1 = stale */ + + get_lock_path(&lock_path, abs_path); + get_pid_path(&pid_path, abs_path); + + strbuf_addf(buf, _("Unable to create '%s': %s.\n\n"), + lock_path.buf, strerror(err)); + + /* + * Try to read PID file unconditionally - it may exist if + * core.lockfilePid was enabled. + */ + if (!read_lock_pid(pid_path.buf, &pid)) { + if (kill((pid_t)pid, 0) == 0 || errno == EPERM) + pid_status = 1; /* running (or no permission to signal) */ + else if (errno == ESRCH) + pid_status = -1; /* no such process - stale lock */ + } + + if (pid_status == 1) + strbuf_addf(buf, _("Lock may be held by process %" PRIuMAX "; " + "if no git process is running, the lock file " + "may be stale (PIDs can be reused)"), + pid); + else if (pid_status == -1) + strbuf_addf(buf, _("Lock was held by process %" PRIuMAX ", " + "which is no longer running; the lock file " + "appears to be stale"), + pid); + else + strbuf_addstr(buf, _("Another git process seems to be running in this repository, " + "or the lock file may be stale")); + + strbuf_release(&lock_path); + strbuf_release(&pid_path); + } else { strbuf_addf(buf, _("Unable to create '%s.lock': %s"), absolute_path(path), strerror(err)); + } } NORETURN void unable_to_lock_die(const char *path, int err) @@ -207,6 +339,8 @@ int commit_lock_file(struct lock_file *lk) { char *result_path = get_locked_file_path(lk); + delete_tempfile(&lk->pid_tempfile); + if (commit_lock_file_to(lk, result_path)) { int save_errno = errno; free(result_path); @@ -216,3 +350,9 @@ int commit_lock_file(struct lock_file *lk) free(result_path); return 0; } + +int rollback_lock_file(struct lock_file *lk) +{ + delete_tempfile(&lk->pid_tempfile); + return delete_tempfile(&lk->tempfile); +} -- cgit v1.3