Hi,
Added to the GFS2 -nmw git tree, thanks. Please remember to add a
Signed-off-by line for future patches - I've added it for you this time,
Steve.
On Fri, 2007-05-04 at 21:49 +0530, Satyam Sharma wrote:
> Hi,
>
> There are the following two trivially-fixed races in fs/dlm/config.c:
>
> 1. The configfs subsystem semaphore must be held by the caller when
> calling config_group_find_obj(). It's needed to walk the subsystem
> hierarchy without racing with a simultaneous mkdir(2) or rmdir(2). I
> looked around to see if there was some other way we were avoiding this
> race, but couldn't find any.
>
> 2. get_comm() does hold the subsystem semaphore but lets go too soon --
> before grabbing a reference on the found config_item. A concurrent
> rmdir(2) could come and release the comm after the up() but before the
> config_item_get().
>
> Patch that fixes both these bugs below.
>
> Cheers,
> S
>
> PS: For some reason, configfs still uses a struct semaphore (as a binary
> semaphore) for configfs_subsystem.su_sem. Someone with free time should
> convert that to a struct mutex, say configfs_subsystem.su_mtx -- which is
> the preferred way to use (binary) mutexes presently. CC'ing Joel Becker on
> this.
>
> ---
>
> Fix two races in fs/dlm/config.c:
>
> (1) Grab the configfs subsystem semaphore before calling
> config_group_find_obj() in get_space(). This solves a potential race
> between get_space() and concurrent mkdir(2) or rmdir(2).
>
> (2) Grab a reference on the found config_item _while_ holding the configfs
> subsystem semaphore in get_comm(), and not after it. This solves a
> potential race between get_comm() and concurrent rmdir(2).
>
> fs/dlm/config.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> Signed-off-by: Satyam Sharma <[email protected]>
>
> ---
>
> diff -ruNp linux-2.6.21.1/fs/dlm/config.c linux-2.6.21.1~patch/fs/dlm/config.c
> --- linux-2.6.21.1/fs/dlm/config.c 2007-04-26 08:38:32.000000000 +0530
> +++ linux-2.6.21.1~patch/fs/dlm/config.c 2007-05-04 21:08:54.000000000 +0530
> @@ -744,9 +744,16 @@ static ssize_t node_weight_write(struct
>
> static struct space *get_space(char *name)
> {
> + struct config_item *i;
> +
> if (!space_list)
> return NULL;
> - return to_space(config_group_find_obj(space_list, name));
> +
> + down(&space_list->cg_subsys->su_sem);
> + i = config_group_find_obj(space_list, name);
> + up(&space_list->cg_subsys->su_sem);
> +
> + return to_space(i);
> }
>
> static void put_space(struct space *sp)
> @@ -772,20 +779,20 @@ static struct comm *get_comm(int nodeid,
> if (cm->nodeid != nodeid)
> continue;
> found = 1;
> + config_item_get(i);
> break;
> } else {
> if (!cm->addr_count ||
> memcmp(cm->addr[0], addr, sizeof(*addr)))
> continue;
> found = 1;
> + config_item_get(i);
> break;
> }
> }
> up(&clusters_root.subsys.su_sem);
>
> - if (found)
> - config_item_get(i);
> - else
> + if (!found)
> cm = NULL;
> return cm;
> }
>
> -
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