cgroups: fix API thinko

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin <[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

What this patch does is add an API for that.

 include/linux/cgroup.h |   11 ++++++++++-
 kernel/cgroup.c        |    9 +++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

include/linux/cgroup.h +10 -1

index 43b2072..b38ec60 100644
@@ -525,7 +525,11 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
-int cgroup_attach_task_current_cg(struct task_struct *);
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}
 
 /*
  * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works

@@ -583,6 +587,11 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
 }
 
 /* No cgroups - nothing to do */
+static inline int cgroup_attach_task_all(struct task_struct *from,
+					 struct task_struct *t)
+{
+	return 0;
+}
 static inline int cgroup_attach_task_current_cg(struct task_struct *t)
 {
 	return 0;

kernel/cgroup.c +5 -4

index dce8ebc..e6293b8 100644
@@ -1606,10 +1606,11 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 }
 
 /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
  * @tsk: the task to be attached
  */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
 	struct cgroupfs_root *root;
 	struct cgroup *cur_cg;

@@ -1617,7 +1618,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
 	cgroup_lock();
 	for_each_active_root(root) {
-		cur_cg = task_cgroup_from_root(current, root);
+		cur_cg = task_cgroup_from_root(from, root);
 		retval = cgroup_attach_task(cur_cg, tsk);
 		if (retval)
 			break;

@@ -1626,7 +1627,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
 	return retval;
 }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
 /*
  * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin <[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

What this patch does is add an API for that.

 include/linux/cgroup.h |   11 ++++++++++-
 kernel/cgroup.c        |    9 +++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

include/linux/cgroup.h +10 -1

index 43b2072..b38ec60 100644
@@ -525,7 +525,11 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
-int cgroup_attach_task_current_cg(struct task_struct *);
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}
 
 /*
  * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works

@@ -583,6 +587,11 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
 }
 
 /* No cgroups - nothing to do */
+static inline int cgroup_attach_task_all(struct task_struct *from,
+					 struct task_struct *t)
+{
+	return 0;
+}
 static inline int cgroup_attach_task_current_cg(struct task_struct *t)
 {
 	return 0;

kernel/cgroup.c +5 -4

index dce8ebc..e6293b8 100644
@@ -1606,10 +1606,11 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 }
 
 /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
  * @tsk: the task to be attached
  */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
 	struct cgroupfs_root *root;
 	struct cgroup *cur_cg;

@@ -1617,7 +1618,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
 	cgroup_lock();
 	for_each_active_root(root) {
-		cur_cg = task_cgroup_from_root(current, root);
+		cur_cg = task_cgroup_from_root(from, root);
 		retval = cgroup_attach_task(cur_cg, tsk);
 		if (retval)
 			break;

@@ -1626,7 +1627,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
 	return retval;
 }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
 /*
  * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

What this patch does is add an API for that.

  include/linux/cgroup.h |   11 ++++++++++-
  kernel/cgroup.c        |    9 +++++----
  2 files changed, 15 insertions(+), 5 deletions(-)

include/linux/cgroup.h +10 -1

index 43b2072..b38ec60 100644
@@ -525,7 +525,11 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
  void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
  int cgroup_scan_tasks(struct cgroup_scanner *scan);
  int cgroup_attach_task(struct cgroup *, struct task_struct *);
-int cgroup_attach_task_current_cg(struct task_struct *);
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}
 
  /*
   * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works

@@ -583,6 +587,11 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
  }
 
  /* No cgroups - nothing to do */
+static inline int cgroup_attach_task_all(struct task_struct *from,
+					 struct task_struct *t)
+{
+	return 0;
+}
  static inline int cgroup_attach_task_current_cg(struct task_struct *t)
  {
  	return 0;

kernel/cgroup.c +3 -2

index dce8ebc..e6293b8 100644
@@ -1606,10 +1606,11 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
  }
 
  /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
   * @tsk: the task to be attached
   */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
  {
  	struct cgroupfs_root *root;
  	struct cgroup *cur_cg;

kernel/cgroup.c +0 -0

  		retval = cgroup_attach_task(cur_cg, tsk);
  		if (retval)

break;

kernel/cgroup.c +1 -1

@@ -1626,7 +1627,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
  	return retval;
  }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
  /*
   * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin <[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

include/linux/cgroup.h +4 -0

+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

What this patch does is add an API for that.

  include/linux/cgroup.h |   11 ++++++++++-
  kernel/cgroup.c        |    9 +++++----
  2 files changed, 15 insertions(+), 5 deletions(-)

include/linux/cgroup.h +10 -1

index 43b2072..b38ec60 100644
@@ -525,7 +525,11 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
  void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
  int cgroup_scan_tasks(struct cgroup_scanner *scan);
  int cgroup_attach_task(struct cgroup *, struct task_struct *);
-int cgroup_attach_task_current_cg(struct task_struct *);
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}
 
  /*
   * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works

@@ -583,6 +587,11 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
  }
 
  /* No cgroups - nothing to do */
+static inline int cgroup_attach_task_all(struct task_struct *from,
+					 struct task_struct *t)
+{
+	return 0;
+}
  static inline int cgroup_attach_task_current_cg(struct task_struct *t)
  {
  	return 0;

kernel/cgroup.c +3 -2

index dce8ebc..e6293b8 100644
@@ -1606,10 +1606,11 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
  }
 
  /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
   * @tsk: the task to be attached
   */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
  {
  	struct cgroupfs_root *root;
  	struct cgroup *cur_cg;

kernel/cgroup.c +0 -0

  		retval = cgroup_attach_task(cur_cg, tsk);
  		if (retval)

break;

kernel/cgroup.c +1 -1

@@ -1626,7 +1627,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
  	return retval;
  }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
  /*
   * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex

Quoted 34 lines · Michael S. Tsirkin

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

Quoted 6 lines

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

So an unprivileged qemu cannot attach vhost thread to its own cgroups. I guess you are planning to make the cgroup_attach_task_all() call in vhost_worker()
to attach itself to the cgroups of qemu.

The new API looks fine, but the
name is little confusing. How about
task_inherit_cgroups(struct task_struct *from, struct task_struct *to)

Quoted 54 lines

What this patch does is add an API for that.

  include/linux/cgroup.h |   11 ++++++++++-
  kernel/cgroup.c        |    9 +++++----
  2 files changed, 15 insertions(+), 5 deletions(-)

include/linux/cgroup.h +10 -1

index 43b2072..b38ec60 100644
@@ -525,7 +525,11 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
  void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
  int cgroup_scan_tasks(struct cgroup_scanner *scan);
  int cgroup_attach_task(struct cgroup *, struct task_struct *);
-int cgroup_attach_task_current_cg(struct task_struct *);
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}
 
  /*
   * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works

@@ -583,6 +587,11 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
  }
 
  /* No cgroups - nothing to do */
+static inline int cgroup_attach_task_all(struct task_struct *from,
+					 struct task_struct *t)
+{
+	return 0;
+}
  static inline int cgroup_attach_task_current_cg(struct task_struct *t)
  {
  	return 0;

kernel/cgroup.c +3 -2

index dce8ebc..e6293b8 100644
@@ -1606,10 +1606,11 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
  }
 
  /**
- * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
+ * @from: attach to all cgroups of a given task
   * @tsk: the task to be attached
   */
-int cgroup_attach_task_current_cg(struct task_struct *tsk)
+int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
  {
  	struct cgroupfs_root *root;
  	struct cgroup *cur_cg;

kernel/cgroup.c int cgroup_attach_task_current_cg(struct task_struct *tsk) · line 1622

Quoted 6 lines

kernel/cgroup.c +1 -1

@@ -1617,7 +1618,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
  	cgroup_lock();
  	for_each_active_root(root) {
-		cur_cg = task_cgroup_from_root(current, root);
+		cur_cg = task_cgroup_from_root(from, root);
 

Now that we are not operating on current, cur_cg should be renamed as from_cg

Quoted 13 lines

kernel/cgroup.c +0 -0

  		retval = cgroup_attach_task(cur_cg, tsk);
  		if (retval)

break;

kernel/cgroup.c +1 -1

@@ -1626,7 +1627,7 @@ int cgroup_attach_task_current_cg(struct task_struct *tsk)
 
  	return retval;
  }
-EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
 
  /*
   * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex

Quoted 35 lines · Sridhar Samudrala

Quoted 34 lines · Michael S. Tsirkin

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

Quoted 5 lines

Quoted 5 lines

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

Quoted 35 lines · Sridhar Samudrala

Quoted 34 lines · Michael S. Tsirkin

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

Quoted 5 lines

Quoted 5 lines

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

So am I correct to assume that this change is now needed in 2.6.36, and unneeded in 2.6.35?

Can it affect the userspace<->kernel API in amy manner?  If so, it should be backported into earlier kernels to reduce the number of incompatible kernels out there.

Paul, did you have any comments?

So am I correct to assume that this change is now needed in 2.6.36, and unneeded in 2.6.35?

Can it affect the userspace<->kernel API in amy manner?  If so, it should be backported into earlier kernels to reduce the number of incompatible kernels out there.

Paul, did you have any comments?

Quoted 36 lines · On Fri, 06 Aug 2010 10:38:24 -0600 Alex Williamson…

Quoted 35 lines · Sridhar Samudrala

Quoted 34 lines · Michael S. Tsirkin

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

Quoted 5 lines

Quoted 5 lines

Quoted 5 lines

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

So am I correct to assume that this change is now needed in 2.6.36, and unneeded in 2.6.35?

Can it affect the userspace<->kernel API in amy manner? If so, it should be backported into earlier kernels to reduce the number of incompatible kernels out there.

Paul, did you have any comments?

I didn't see any update in response to the minor review comments, so...

 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |    6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff -puN include/linux/cgroup.h~cgroups-fix-api-thinko-fix include/linux/cgroup.h

include/linux/cgroup.h renamed from include/linux/cgroup.h~cgroups-fix-api-thinko-fix +1 -0

@@ -579,6 +579,7 @@ void cgroup_iter_end(struct cgroup *cgrp
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+
 static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
 {
 	return cgroup_attach_task_all(current, tsk);

diff -puN kernel/cgroup.c~cgroups-fix-api-thinko-fix kernel/cgroup.c

kernel/cgroup.c renamed from kernel/cgroup.c~cgroups-fix-api-thinko-fix +3 -3

@@ -1798,13 +1798,13 @@ out:
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
 	struct cgroupfs_root *root;
-	struct cgroup *cur_cg;
 	int retval = 0;
 
 	cgroup_lock();
 	for_each_active_root(root) {
-		cur_cg = task_cgroup_from_root(from, root);
-		retval = cgroup_attach_task(cur_cg, tsk);
+		struct cgroup *from_cg = task_cgroup_from_root(from, root);
+
+		retval = cgroup_attach_task(from_cg, tsk);
 		if (retval)
 			break;
 	}

_

Quoted 36 lines · On Fri, 06 Aug 2010 10:38:24 -0600 Alex Williamson…

Quoted 35 lines · Sridhar Samudrala

Quoted 34 lines · Michael S. Tsirkin

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin<[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

Thanks!

This patch is on top of net-next, it is needed for fix vhost-net regression in net-next, where a non-priveledged process can't enable the device anymore:

Quoted 5 lines

Quoted 5 lines

Quoted 5 lines

when qemu uses vhost, inside the ioctl call it creates a thread, and tries to add
this thread to the groups of current, and it fails. But we control the thread, so to solve the problem, we really should tell it 'connect to out cgroups'.

So am I correct to assume that this change is now needed in 2.6.36, and unneeded in 2.6.35?

Can it affect the userspace<->kernel API in amy manner? If so, it should be backported into earlier kernels to reduce the number of incompatible kernels out there.

Paul, did you have any comments?

I didn't see any update in response to the minor review comments, so...

 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |    6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff -puN include/linux/cgroup.h~cgroups-fix-api-thinko-fix include/linux/cgroup.h

include/linux/cgroup.h renamed from include/linux/cgroup.h~cgroups-fix-api-thinko-fix +1 -0

@@ -579,6 +579,7 @@ void cgroup_iter_end(struct cgroup *cgrp
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
+
 static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
 {
 	return cgroup_attach_task_all(current, tsk);

diff -puN kernel/cgroup.c~cgroups-fix-api-thinko-fix kernel/cgroup.c

kernel/cgroup.c renamed from kernel/cgroup.c~cgroups-fix-api-thinko-fix +3 -3

@@ -1798,13 +1798,13 @@ out:
 int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
 {
 	struct cgroupfs_root *root;
-	struct cgroup *cur_cg;
 	int retval = 0;
 
 	cgroup_lock();
 	for_each_active_root(root) {
-		cur_cg = task_cgroup_from_root(from, root);
-		retval = cgroup_attach_task(cur_cg, tsk);
+		struct cgroup *from_cg = task_cgroup_from_root(from, root);
+
+		retval = cgroup_attach_task(from_cg, tsk);
 		if (retval)
 			break;
 	}

_

cgroup_attach_task_current_cg API that have upstream is backwards: we really need an API to attach to the cgroups from another process A to the current one.

In our case (vhost), a priveledged user wants to attach it's task to cgroups from a less priveledged one, the API makes us run it in the other task's context, and this fails.

So let's make the API generic and just pass in 'from' and 'to' tasks. Add an inline wrapper for cgroup_attach_task_current_cg to avoid breaking bisect.

Signed-off-by Michael S. Tsirkin <[email protected]>

---

Paul, Li, Sridhar, could you please review the following patch?

I only compile-tested it due to travel, but looks straight-forward to me.
Alex Williamson volunteered to test and report the results. Sending out now for review as I might be offline for a bit. Will only try to merge when done, obviously.

If OK, I would like to merge this through -net tree, together with the patch fixing vhost-net. Let me know if that sounds ok.

include/linux/cgroup.h +4 -0

+static inline int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	return cgroup_attach_task_all(current, tsk);
+}