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Fix race condition with zed pidfile creation

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When the zed is started as a forking daemon (by default),
a race-condition exists where the parent process can terminate before
the pidfile has been created by the grandchild process.  When invoked
as a Type=forking systemd service, this can result in the following:

  systemd[1]: Starting ZFS Event Daemon (zed)...
  systemd[1]: PID file /var/run/zed.pid not readable (yet?) after start.

This commit adds a daemonize pipe to allow the grandchild process to
signal the parent process that initialization is complete (and the
pidfile has been created).  The parent process will wait for this
notification before exiting.

Signed-off-by: Chris Dunlap <cdunlap@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #2252
This commit is contained in:
Chris Dunlap
2014-08-27 13:18:01 -07:00
committed by Brian Behlendorf
parent 6c3c3387b1
commit 5a8855b716
4 changed files with 184 additions and 22 deletions
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cmd/zed/zed_log.c
+95
View File
@@ -25,6 +25,7 @@
*/
#include <assert.h>
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
@@ -40,6 +41,7 @@ static struct {
unsigned do_syslog:1;
int level;
char id[ZED_LOG_MAX_ID_LEN];
int pipe_fd[2];
} _ctx;
void
@@ -53,6 +55,8 @@ zed_log_init(const char *identity)
} else {
_ctx.id[0] = '\0';
}
_ctx.pipe_fd[0] = -1;
_ctx.pipe_fd[1] = -1;
}
void
@@ -63,6 +67,97 @@ zed_log_fini()
}
}
/*
* Create pipe for communicating daemonization status between the parent and
* child processes across the double-fork().
*/
void
zed_log_pipe_open(void)
{
if ((_ctx.pipe_fd[0] != -1) || (_ctx.pipe_fd[1] != -1))
zed_log_die("Invalid use of zed_log_pipe_open in PID %d",
(int) getpid());
if (pipe(_ctx.pipe_fd) < 0)
zed_log_die("Failed to create daemonize pipe in PID %d: %s",
(int) getpid(), strerror(errno));
}
/*
* Close the read-half of the daemonize pipe.
* This should be called by the child after fork()ing from the parent since
* the child will never read from this pipe.
*/
void
zed_log_pipe_close_reads(void)
{
if (_ctx.pipe_fd[0] < 0)
zed_log_die(
"Invalid use of zed_log_pipe_close_reads in PID %d",
(int) getpid());
if (close(_ctx.pipe_fd[0]) < 0)
zed_log_die(
"Failed to close reads on daemonize pipe in PID %d: %s",
(int) getpid(), strerror(errno));
_ctx.pipe_fd[0] = -1;
}
/*
* Close the write-half of the daemonize pipe.
* This should be called by the parent after fork()ing its child since the
* parent will never write to this pipe.
* This should also be called by the child once initialization is complete
* in order to signal the parent that it can safely exit.
*/
void
zed_log_pipe_close_writes(void)
{
if (_ctx.pipe_fd[1] < 0)
zed_log_die(
"Invalid use of zed_log_pipe_close_writes in PID %d",
(int) getpid());
if (close(_ctx.pipe_fd[1]) < 0)
zed_log_die(
"Failed to close writes on daemonize pipe in PID %d: %s",
(int) getpid(), strerror(errno));
_ctx.pipe_fd[1] = -1;
}
/*
* Block on reading from the daemonize pipe until signaled by the child
* (via zed_log_pipe_close_writes()) that initialization is complete.
* This should only be called by the parent while waiting to exit after
* fork()ing the child.
*/
void
zed_log_pipe_wait(void)
{
ssize_t n;
char c;
if (_ctx.pipe_fd[0] < 0)
zed_log_die("Invalid use of zed_log_pipe_wait in PID %d",
(int) getpid());
for (;;) {
n = read(_ctx.pipe_fd[0], &c, sizeof (c));
if (n < 0) {
if (errno == EINTR)
continue;
zed_log_die(
"Failed to read from daemonize pipe in PID %d: %s",
(int) getpid(), strerror(errno));
}
if (n == 0) {
break;
}
}
}
void
zed_log_stderr_open(int level)
{