Hi Manfred,
On Mon, 2013-09-30 at 11:13 +0200, Manfred Spraul wrote:
> After acquiring the semlock spinlock, the operations must test that the
> array is still valid.
>
> - semctl() and exit_sem() would walk stale linked lists (ugly, but should
> be ok: all lists are empty)
>
> - semtimedop() would sleep forever - and if woken up due to a signal -
> access memory after free.
Yep, that was next on my list - I had a patch for semtimedop() but was
waiting to rebase it on top of your previous changes. Anyway thanks for
sending this.
>
> The patch standardizes the tests for .deleted, so that all tests in one
> function leave the function with the same approach.
>
> Right now, it's a mixture of "goto cleanup", some cleanup and then
> "goto further_cleanup" and all cleanup+"return -EIDRM" - that makes the
> review much harder.
>
> Davidlohr: Could you please review the patch?
> I did some stress test, but probably I didn't hit exactly the modified
> lines.
This shouldn't affect performance, if that's what you mean. One more
read in the critical region won't make any difference. The patch looks
good, just one doubt below.
> Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
> ---
> ipc/sem.c | 43 ++++++++++++++++++++++++++++++-------------
> 1 file changed, 30 insertions(+), 13 deletions(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 19c8b98..a2fa795 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1229,6 +1229,12 @@ static int semctl_setval(struct ipc_namespace *ns, int
> semid, int semnum,
>
> sem_lock(sma, NULL, -1);
>
> + if (sma->sem_perm.deleted) {
> + sem_unlock(sma, -1);
> + rcu_read_unlock();
> + return -EIDRM;
> + }
> +
> curr = &sma->sem_base[semnum];
>
> ipc_assert_locked_object(&sma->sem_perm);
> @@ -1285,10 +1291,8 @@ static int semctl_main(struct ipc_namespace *ns, int
> semid, int semnum,
> sem_lock(sma, NULL, -1);
> if(nsems > SEMMSL_FAST) {
> if (!ipc_rcu_getref(sma)) {
> - sem_unlock(sma, -1);
> - rcu_read_unlock();
> err = -EIDRM;
> - goto out_free;
> + goto out_unlock;
> }
> sem_unlock(sma, -1);
> rcu_read_unlock();
> @@ -1301,10 +1305,13 @@ static int semctl_main(struct ipc_namespace *ns, int
> semid, int semnum,
> rcu_read_lock();
> sem_lock_and_putref(sma);
> if (sma->sem_perm.deleted) {
> - sem_unlock(sma, -1);
> - rcu_read_unlock();
> err = -EIDRM;
> - goto out_free;
> + goto out_unlock;
> + }
> + } else {
> + if (sma->sem_perm.deleted) {
> + err = -EIDRM;
> + goto out_unlock;
> }
I'm a bit lost here. Why should we only check the existence of the sem
if nsems <= SEMMSL_FAST? Shouldn't the same should apply either way?
Thanks,
Davidlohr
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
