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Re: [libvirt] [PATCH] Avoid deadlock on logging mutex due to fork in virFileCreate/virDirCreate.



On Wed, Feb 03, 2010 at 10:27:32AM -0500, Laine Stump wrote:
> These functions have the same potential problem that Cole found in
> virExec - if the log mutex is currently held at the time of the fork,
> the child process' logging mutex will be locked, but nobody in the
> process to unlock it. If the child process tries to log anything, it
> will wait forever for this lock. The solution is to have the parent
> acquire the lock before fork, then both parent and child release the
> lock right after.
> 
> Note that this patch requires Cole's patch to be applied first.
> ---
>  src/util/util.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/src/util/util.c b/src/util/util.c
> index 901c0d2..d8a2394 100644
> --- a/src/util/util.c
> +++ b/src/util/util.c
> @@ -1263,7 +1263,11 @@ int virFileCreate(const char *path, mode_t mode,
>       * following dance avoids problems caused by root-squashing
>       * NFS servers. */
>  
> -    if ((pid = fork()) < 0) {
> +    virLogLock();
> +    pid = fork();
> +    virLogUnlock();
> +
> +    if (pid < 0) {
>          ret = errno;
>          virReportSystemError(NULL, errno,
>                               _("cannot fork o create file '%s'"), path);
> @@ -1369,7 +1373,11 @@ int virDirCreate(const char *path, mode_t mode,
>          return virDirCreateSimple(path, mode, uid, gid, flags);
>      }
>  
> -    if ((pid = fork()) < 0) {
> +    virLogLock();
> +    pid = fork();
> +    virLogUnlock();
> +
> +    if (pid < 0) {
>          ret = errno;
>          virReportSystemError(NULL, errno,
>                               _("cannot fork to create directory '%s'"),

  Okay, makes sense, ACK, and applied !
Maybe at some point a wrapper around fork() may be nicer.

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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