Date: Wed, 13 Mar 2013 11:18:36 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Dirk Engling <erdgeist@erdgeist.org> Subject: Re: pidfile_open incorrectly returns EAGAIN when pidfile is locked Message-ID: <201303131118.36811.jhb@freebsd.org> In-Reply-To: <513F8D20.2050707@erdgeist.org> References: <513F8D20.2050707@erdgeist.org>
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On Tuesday, March 12, 2013 4:16:32 pm Dirk Engling wrote:
> While debugging my own daemon I noticed that pidfile_open does not
> perform the appropriate checks for a running daemon if the caller does
> not provide a pidptr to pidfile_open
>
> fd = flopen(pfh->pf_path,
> O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_NONBLOCK, mode);
>
> fails when another daemon holds the lock and flopen sets errno to
> EAGAIN, the check 4 lines below in
>
> if (errno == EWOULDBLOCK && pidptr != NULL) {
>
> means that the pidfile_read is never executed.
>
> This results in my second daemon receiving an EAGAIN which clearly was
> meant to report a race condition between two daemons starting at the
> same time and the first one not yet finishing pidfile_write.
>
> The expected behavior would be to set errno to EEXIST, even if no pidptr
> was passed.
Yes, I think it should actually perform the same logic even if pidptr is
NULL of waiting for the other daemon to finish starting up. Something like
this:
Index: lib/libutil/pidfile.c
===================================================================
--- pidfile.c (revision 248162)
+++ pidfile.c (working copy)
@@ -100,6 +100,7 @@ pidfile_open(const char *path, mode_t mode, pid_t
struct stat sb;
int error, fd, len, count;
struct timespec rqtp;
+ pid_t dummy;
pfh = malloc(sizeof(*pfh));
if (pfh == NULL)
@@ -126,7 +127,9 @@ pidfile_open(const char *path, mode_t mode, pid_t
fd = flopen(pfh->pf_path,
O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_NONBLOCK, mode);
if (fd == -1) {
- if (errno == EWOULDBLOCK && pidptr != NULL) {
+ if (errno == EWOULDBLOCK) {
+ if (pidptr == NULL)
+ pidptr = &dummy;
count = 20;
rqtp.tv_sec = 0;
rqtp.tv_nsec = 5000000;
--
John Baldwin
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