Mandeep Singh Baines wrote: > Since cgroup_attach_proc is protected by a threadgroup_lock, we > can replace the tasklist_lock in cgroup_attach_proc with an > rcu_read_lock. > To keep the complexity of the double-check locking > in one place, I also moved the thread_group_leader check up into > attach_task_by_pid. This allows us to use a goto instead of > returning -EAGAIN. Please split it into 2 patches, so each patch does one and only one thing. > > While at it, also converted a couple of returns to gotos. > > Changes in V3: > * https://lkml.org/lkml/2011/12/22/419 (Frederic Weisbecker) > * Add an rcu_read_lock to protect against exit > Changes in V2: > * https://lkml.org/lkml/2011/12/22/86 (Tejun Heo) > * Use a goto instead of returning -EAGAIN > > Suggested-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> > Signed-off-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Li Zefan <lizf@xxxxxxxxxxxxxx> > Cc: containers@xxxxxxxxxxxxxxxxxxxxxxxxxx > Cc: cgroups@xxxxxxxxxxxxxxx > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: Oleg Nesterov <oleg@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Paul Menage <paul@xxxxxxxxxxxxxx> > --- > kernel/cgroup.c | 74 +++++++++++++++++++----------------------------------- > 1 files changed, 26 insertions(+), 48 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 1042b3c..6ee1438 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -2102,21 +2102,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) > if (retval) > goto out_free_group_list; > > - /* prevent changes to the threadgroup list while we take a snapshot. */ > - read_lock(&tasklist_lock); > - if (!thread_group_leader(leader)) { > - /* > - * a race with de_thread from another thread's exec() may strip > - * us of our leadership, making while_each_thread unsafe to use > - * on this task. if this happens, there is no choice but to > - * throw this task away and try again (from cgroup_procs_write); > - * this is "double-double-toil-and-trouble-check locking". > - */ > - read_unlock(&tasklist_lock); > - retval = -EAGAIN; > - goto out_free_group_list; > - } > - > + rcu_read_lock(); > tsk = leader; > i = 0; > do { > @@ -2145,7 +2131,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) > group_size = i; > tset.tc_array = group; > tset.tc_array_len = group_size; > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > > /* methods shouldn't be called if no task is actually migrating */ > retval = 0; > @@ -2242,22 +2228,14 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) > if (!cgroup_lock_live_group(cgrp)) > return -ENODEV; > > +retry_find_task: > if (pid) { > rcu_read_lock(); > tsk = find_task_by_vpid(pid); > if (!tsk) { > rcu_read_unlock(); > - cgroup_unlock(); > - return -ESRCH; > - } > - if (threadgroup) { > - /* > - * RCU protects this access, since tsk was found in the > - * tid map. a race with de_thread may cause group_leader > - * to stop being the leader, but cgroup_attach_proc will > - * detect it later. > - */ > - tsk = tsk->group_leader; > + ret= -ESRCH; ret = -ESRCH; > + goto out_unlock_cgroup; > } > /* > * even if we're attaching all tasks in the thread group, we _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
