[PATCH v2 1/1] exportfs: Stop racing exportfs on clusters

[PATCH v2 1/1] exportfs: Stop racing exportfs on clusters

[Steve Dickson]

This problem can occur when multiple cluster services fail over
at the same time, causing missing high-available exports.
Having a lot of nfs-exports will trigger this issue easier.

https://bugzilla.linux-nfs.org/show_bug.cgi?id=224

Signed-off-by: Steve Dickson <steved@redhat.com>
---
 support/include/exportfs.h |    4 ++++
 utils/exportfs/exportfs.c  |   41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 0 deletions(-)

diff --git a/support/include/exportfs.h b/support/include/exportfs.h
index 01e87dd..99916e5 100644
--- a/support/include/exportfs.h
+++ b/support/include/exportfs.h
@@ -32,6 +32,10 @@ enum {
 	FSLOC_STUB
 };
 
+#ifndef EXP_LOCKFILE
+#define EXP_LOCKFILE "/var/lib/nfs/export-lock"
+#endif
+
 typedef struct mclient {
 	struct mclient *	m_next;
 	char *			m_hostname;
diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index 7432a65..7326802 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -16,6 +16,7 @@
 #include <sys/stat.h>
 #include <sys/vfs.h>
 #include <sys/stat.h>
+#include <sys/file.h>
 #include <unistd.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -44,6 +45,39 @@ static void	validate_export(nfs_export *exp);
 static int	matchhostname(const char *hostname1, const char *hostname2);
 static void	export_d_read(const char *dname);
 
+static const char *lockfile = EXP_LOCKFILE;
+static int _lockfd = -1;
+
+/*
+ * If we aren't careful, changes made by exportfs can be lost
+ * when multiple exports process run at once:
+ *
+ *	exportfs process 1	exportfs process 2
+ *	------------------------------------------
+ *	reads etab version A	reads etab version A
+ *	adds new export B	adds new export C
+ *	writes A+B		writes A+C
+ *
+ * The locking in support/export/xtab.c will prevent mountd from
+ * seeing a partially written version of etab, and will prevent 
+ * the two writers above from writing simultaneously and
+ * corrupting etab, but to prevent problems like the above we
+ * need these additional lockfile() routines.
+ */
+void 
+grab_lockfile()
+{
+	_lockfd = open(lockfile, O_CREAT|O_RDWR, 0666);
+	if (_lockfd != -1) 
+		lockf(_lockfd, F_LOCK, 0);
+}
+void 
+release_lockfile()
+{
+	if (_lockfd != -1)
+		lockf(_lockfd, F_ULOCK, 0);
+}
+
 int
 main(int argc, char **argv)
 {
@@ -129,6 +163,13 @@ main(int argc, char **argv)
 			return 0;
 		}
 	}
+
+	/*
+	 * Serialize things as best we can
+	 */
+	grab_lockfile();
+	atexit(release_lockfile);
+
 	if (f_export && ! f_ignore) {
 		export_read(_PATH_EXPORTS);
 		export_d_read(_PATH_EXPORTS_D);
-- 
1.7.7.5

Re: [PATCH v2 1/1] exportfs: Stop racing exportfs on clusters

[Steve Dickson]

On 03/12/2012 01:23 PM, Steve Dickson wrote:
> This problem can occur when multiple cluster services fail over
> at the same time, causing missing high-available exports.
> Having a lot of nfs-exports will trigger this issue easier.
> 
> https://bugzilla.linux-nfs.org/show_bug.cgi?id=224
> 
> Signed-off-by: Steve Dickson <steved@redhat.com>
Committed... 

steved.

> ---
>  support/include/exportfs.h |    4 ++++
>  utils/exportfs/exportfs.c  |   41 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+), 0 deletions(-)
> 
> diff --git a/support/include/exportfs.h b/support/include/exportfs.h
> index 01e87dd..99916e5 100644
> --- a/support/include/exportfs.h
> +++ b/support/include/exportfs.h
> @@ -32,6 +32,10 @@ enum {
>  	FSLOC_STUB
>  };
>  
> +#ifndef EXP_LOCKFILE
> +#define EXP_LOCKFILE "/var/lib/nfs/export-lock"
> +#endif
> +
>  typedef struct mclient {
>  	struct mclient *	m_next;
>  	char *			m_hostname;
> diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
> index 7432a65..7326802 100644
> --- a/utils/exportfs/exportfs.c
> +++ b/utils/exportfs/exportfs.c
> @@ -16,6 +16,7 @@
>  #include <sys/stat.h>
>  #include <sys/vfs.h>
>  #include <sys/stat.h>
> +#include <sys/file.h>
>  #include <unistd.h>
>  #include <stdbool.h>
>  #include <stdlib.h>
> @@ -44,6 +45,39 @@ static void	validate_export(nfs_export *exp);
>  static int	matchhostname(const char *hostname1, const char *hostname2);
>  static void	export_d_read(const char *dname);
>  
> +static const char *lockfile = EXP_LOCKFILE;
> +static int _lockfd = -1;
> +
> +/*
> + * If we aren't careful, changes made by exportfs can be lost
> + * when multiple exports process run at once:
> + *
> + *	exportfs process 1	exportfs process 2
> + *	------------------------------------------
> + *	reads etab version A	reads etab version A
> + *	adds new export B	adds new export C
> + *	writes A+B		writes A+C
> + *
> + * The locking in support/export/xtab.c will prevent mountd from
> + * seeing a partially written version of etab, and will prevent 
> + * the two writers above from writing simultaneously and
> + * corrupting etab, but to prevent problems like the above we
> + * need these additional lockfile() routines.
> + */
> +void 
> +grab_lockfile()
> +{
> +	_lockfd = open(lockfile, O_CREAT|O_RDWR, 0666);
> +	if (_lockfd != -1) 
> +		lockf(_lockfd, F_LOCK, 0);
> +}
> +void 
> +release_lockfile()
> +{
> +	if (_lockfd != -1)
> +		lockf(_lockfd, F_ULOCK, 0);
> +}
> +
>  int
>  main(int argc, char **argv)
>  {
> @@ -129,6 +163,13 @@ main(int argc, char **argv)
>  			return 0;
>  		}
>  	}
> +
> +	/*
> +	 * Serialize things as best we can
> +	 */
> +	grab_lockfile();
> +	atexit(release_lockfile);
> +
>  	if (f_export && ! f_ignore) {
>  		export_read(_PATH_EXPORTS);
>  		export_d_read(_PATH_EXPORTS_D);