[Mesa-dev] [PATCH] winsys/sw/xlib: Prevent shared memory segment leakage.

[Ian Romanick]

On 04/24/2013 11:23 AM, jfonseca at vmware.com wrote:
> From: José Fonseca <jfonseca at vmware.com>
>
> Running piglit with was causing all sort of weird stuff happening to my
> desktop (Chromium webpages become blank, Qt Creator flickered, etc).  I
> tracked this down to shared memory segment leakage when GL is not shutdown
> properly. The segments can be seen running `ipcs` and looking for
> nattch==0.
>
> This changes fixes this by calling shmctl(IPC_RMID) soon after creation
> (which does not remove the segment immediately, but simply marks it for
> removal when no more processes are attached).
>
> src/mesa/drivers/x11/xm_buffer.c also does something similar, albeit
> slightly later in time -- after XShmCreateImage() call --, but calling
> shmctl(IPC_RMID) before XShmCreateImage() seems to work equally well,
> with fewer chances of leaking the shared memory segment.
>
> NOTE: This is a candidate for stable branches.
> ---
>   src/gallium/winsys/sw/xlib/xlib_sw_winsys.c |   11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c b/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
> index 3aef8da..584fbee 100644
> --- a/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
> +++ b/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
> @@ -131,8 +131,13 @@ alloc_shm(struct xlib_displaytarget *buf, unsigned size)
>      }
>
>      shminfo->shmaddr = (char *) shmat(shminfo->shmid, 0, 0);
> +
> +   /* Mark the segment to be destroyed, so that it is automatically destroyed
> +    * when this process dies.
> +    */
> +   shmctl(shminfo->shmid, IPC_RMID, 0);
> +
>      if (shminfo->shmaddr == (char *) -1) {
> -      shmctl(shminfo->shmid, IPC_RMID, 0);
>         return NULL;
>      }
>
> @@ -165,6 +170,8 @@ alloc_shm_ximage(struct xlib_displaytarget *xlib_dt,
>                                         &xlib_dt->shminfo,
>                                         width, height);
>      if (xlib_dt->tempImage == NULL) {
> +
> +	   debug_printf("XShmCreateImage failed\n");

Did you intend the extra debug_printf still be around?

>         xlib_dt->shm = False;
>         return;
>      }
> @@ -177,6 +184,7 @@ alloc_shm_ximage(struct xlib_displaytarget *xlib_dt,
>      XSync(xlib_dt->display, False);
>
>      if (XErrorFlag) {
> +	   debug_printf("XErrorFlag set\n");
>         /* we are on a remote display, this error is normal, don't print it */
>         XFlush(xlib_dt->display);
>         XErrorFlag = 0;
> @@ -251,7 +259,6 @@ xlib_displaytarget_destroy(struct sw_winsys *ws,
>      if (xlib_dt->data) {
>         if (xlib_dt->shminfo.shmid >= 0) {
>            shmdt(xlib_dt->shminfo.shmaddr);
> -         shmctl(xlib_dt->shminfo.shmid, IPC_RMID, 0);
>
>            xlib_dt->shminfo.shmid = -1;
>            xlib_dt->shminfo.shmaddr = (char *) -1;
>