On Mon, Feb 7, 2011 at 5:37 PM, Ben Blum <bblum@xxxxxxxxxxxxxx> wrote:
> Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
>
> From: Ben Blum <bblum@xxxxxxxxxxxxxx>
>
> This patch adds an rwsem that lives in a threadgroup's signal_struct that's
> taken for reading in the fork path, under CONFIG_CGROUPS. If another part of
> the kernel later wants to use such a locking mechanism, the CONFIG_CGROUPS
> ifdefs should be changed to a higher-up flag that CGROUPS and the other system
> would both depend on.
>
> This is a pre-patch for cgroup-procs-write.patch.
>
> Signed-off-by: Ben Blum <bblum@xxxxxxxxxxxxxx>
Reviewed-by: Paul Menage <menage@xxxxxxxxxx>
AFAICS, the only change from the previous version of this patch is the
addition of including linux/rwsem.h in sched.h, so I think it's fair
to assume my previous Reviewed-by: tag still holds.
(Incidentally, does anyone have any handy tools for tracking diffs
between things you've previously tagged as Acked or Reviewed-by, and
newer versions?
Paul
> ---
> include/linux/init_task.h | 9 +++++++++
> include/linux/sched.h | 37 +++++++++++++++++++++++++++++++++++++
> kernel/fork.c | 10 ++++++++++
> 3 files changed, 56 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> index 6b281fa..b560381 100644
> --- a/include/linux/init_task.h
> +++ b/include/linux/init_task.h
> @@ -15,6 +15,14 @@
> extern struct files_struct init_files;
> extern struct fs_struct init_fs;
>
> +#ifdef CONFIG_CGROUPS
> +#define INIT_THREADGROUP_FORK_LOCK(sig) \
> + .threadgroup_fork_lock = \
> + __RWSEM_INITIALIZER(sig.threadgroup_fork_lock),
> +#else
> +#define INIT_THREADGROUP_FORK_LOCK(sig)
> +#endif
> +
> #define INIT_SIGNALS(sig) { \
> .nr_threads = 1, \
> .wait_chldexit = __WAIT_QUEUE_HEAD_INITIALIZER(sig.wait_chldexit),\
> @@ -31,6 +39,7 @@ extern struct fs_struct init_fs;
> }, \
> .cred_guard_mutex = \
> __MUTEX_INITIALIZER(sig.cred_guard_mutex), \
> + INIT_THREADGROUP_FORK_LOCK(sig) \
> }
>
> extern struct nsproxy init_nsproxy;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 8580dc6..2fdbeb1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -509,6 +509,8 @@ struct thread_group_cputimer {
> spinlock_t lock;
> };
>
> +#include <linux/rwsem.h>
> +
> /*
> * NOTE! "signal_struct" does not have it's own
> * locking, because a shared signal_struct always
> @@ -623,6 +625,16 @@ struct signal_struct {
> unsigned audit_tty;
> struct tty_audit_buf *tty_audit_buf;
> #endif
> +#ifdef CONFIG_CGROUPS
> + /*
> + * The threadgroup_fork_lock prevents threads from forking with
> + * CLONE_THREAD while held for writing. Use this for fork-sensitive
> + * threadgroup-wide operations. It's taken for reading in fork.c in
> + * copy_process().
> + * Currently only needed write-side by cgroups.
> + */
> + struct rw_semaphore threadgroup_fork_lock;
> +#endif
>
> int oom_adj; /* OOM kill score adjustment (bit shift) */
> int oom_score_adj; /* OOM kill score adjustment */
> @@ -2270,6 +2282,31 @@ static inline void unlock_task_sighand(struct task_struct *tsk,
> spin_unlock_irqrestore(&tsk->sighand->siglock, *flags);
> }
>
> +/* See the declaration of threadgroup_fork_lock in signal_struct. */
> +#ifdef CONFIG_CGROUPS
> +static inline void threadgroup_fork_read_lock(struct task_struct *tsk)
> +{
> + down_read(&tsk->signal->threadgroup_fork_lock);
> +}
> +static inline void threadgroup_fork_read_unlock(struct task_struct *tsk)
> +{
> + up_read(&tsk->signal->threadgroup_fork_lock);
> +}
> +static inline void threadgroup_fork_write_lock(struct task_struct *tsk)
> +{
> + down_write(&tsk->signal->threadgroup_fork_lock);
> +}
> +static inline void threadgroup_fork_write_unlock(struct task_struct *tsk)
> +{
> + up_write(&tsk->signal->threadgroup_fork_lock);
> +}
> +#else
> +static inline void threadgroup_fork_read_lock(struct task_struct *tsk) {}
> +static inline void threadgroup_fork_read_unlock(struct task_struct *tsk) {}
> +static inline void threadgroup_fork_write_lock(struct task_struct *tsk) {}
> +static inline void threadgroup_fork_write_unlock(struct task_struct *tsk) {}
> +#endif
> +
> #ifndef __HAVE_THREAD_FUNCTIONS
>
> #define task_thread_info(task) ((struct thread_info *)(task)->stack)
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0979527..aefe61f 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -905,6 +905,10 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
>
> tty_audit_fork(sig);
>
> +#ifdef CONFIG_CGROUPS
> + init_rwsem(&sig->threadgroup_fork_lock);
> +#endif
> +
> sig->oom_adj = current->signal->oom_adj;
> sig->oom_score_adj = current->signal->oom_score_adj;
> sig->oom_score_adj_min = current->signal->oom_score_adj_min;
> @@ -1087,6 +1091,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> monotonic_to_bootbased(&p->real_start_time);
> p->io_context = NULL;
> p->audit_context = NULL;
> + if (clone_flags & CLONE_THREAD)
> + threadgroup_fork_read_lock(current);
> cgroup_fork(p);
> #ifdef CONFIG_NUMA
> p->mempolicy = mpol_dup(p->mempolicy);
> @@ -1294,6 +1300,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> write_unlock_irq(&tasklist_lock);
> proc_fork_connector(p);
> cgroup_post_fork(p);
> + if (clone_flags & CLONE_THREAD)
> + threadgroup_fork_read_unlock(current);
> perf_event_fork(p);
> return p;
>
> @@ -1332,6 +1340,8 @@ bad_fork_cleanup_policy:
> mpol_put(p->mempolicy);
> bad_fork_cleanup_cgroup:
> #endif
> + if (clone_flags & CLONE_THREAD)
> + threadgroup_fork_read_unlock(current);
> cgroup_exit(p, cgroup_callbacks_done);
> delayacct_tsk_free(p);
> module_put(task_thread_info(p)->exec_domain->module);
>
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