[SRU][Xenial][PATCH 0/1] block: fix module reference leak on put_disk() call for cgroups throttle

Previous Topic Next Topic
 
classic Classic list List threaded Threaded
5 messages Options
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

[SRU][Xenial][PATCH 0/1] block: fix module reference leak on put_disk() call for cgroups throttle

Joseph Salisbury-3
BugLink: http://bugs.launchpad.net/bugs/1683976

== SRU Justification ==
Due to this bug, the module reference count will leak whenever you write to
/sys/fs/cgroup/blkio/blkio.throttle.*  There is a script in the bug report
to reproduce the bug.

Commit 39a169b62b41 resolves this bug and was added to mainline in
v4.5-rc5.  However, it was not cc'd to stable.

This commit is also needed in Trusty, but needs a minor backport.  The Trusty
SRU will be sent separately.

== Fix ==
commit 39a169b62b415390398291080dafe63aec751e0a
Author: Roman Pen <[hidden email]>
Date:   Tue Feb 9 12:33:35 2016 -0700

    block: fix module reference leak on put_disk() call for cgroups throttle

== Test Case ==
A test kernel was built with this patch and tested by the original bug reporter.
The bug reporter states the test kernel resolved the bug.


Roman Pen (1):
  block: fix module reference leak on put_disk() call for cgroups
    throttle

 block/blk-cgroup.c | 9 +++++++++
 1 file changed, 9 insertions(+)

--
2.7.4


--
kernel-team mailing list
[hidden email]
https://lists.ubuntu.com/mailman/listinfo/kernel-team
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

[SRU][Xenial][PATCH 1/1] block: fix module reference leak on put_disk() call for cgroups throttle

Joseph Salisbury-3
From: Roman Pen <[hidden email]>

BugLink: http://bugs.launchpad.net/bugs/1683976

get_disk(),get_gendisk() calls have non explicit side effect: they
increase the reference on the disk owner module.

The following is the correct sequence how to get a disk reference and
to put it:

    disk = get_gendisk(...);

    /* use disk */

    owner = disk->fops->owner;
    put_disk(disk);
    module_put(owner);

fs/block_dev.c is aware of this required module_put() call, but f.e.
blkg_conf_finish(), which is located in block/blk-cgroup.c, does not put
a module reference.  To see a leakage in action cgroups throttle config
can be used.  In the following script I'm removing throttle for /dev/ram0
(actually this is NOP, because throttle was never set for this device):

    # lsmod | grep brd
    brd                     5175  0
    # i=100; while [ $i -gt 0 ]; do echo "1:0 0" > \
        /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device; i=$(($i - 1)); \
    done
    # lsmod | grep brd
    brd                     5175  100

Now brd module has 100 references.

The issue is fixed by calling module_put() just right away put_disk().

Signed-off-by: Roman Pen <[hidden email]>
Cc: Gi-Oh Kim <[hidden email]>
Cc: Tejun Heo <[hidden email]>
Cc: Jens Axboe <[hidden email]>
Cc: [hidden email]
Cc: [hidden email]
Signed-off-by: Jens Axboe <[hidden email]>
(cherry picked from commit 39a169b62b415390398291080dafe63aec751e0a)
Signed-off-by: Joseph Salisbury <[hidden email]>
---
 block/blk-cgroup.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 9d359e0..8161090 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -788,6 +788,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 {
  struct gendisk *disk;
  struct blkcg_gq *blkg;
+ struct module *owner;
  unsigned int major, minor;
  int key_len, part, ret;
  char *body;
@@ -804,7 +805,9 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
  if (!disk)
  return -ENODEV;
  if (part) {
+ owner = disk->fops->owner;
  put_disk(disk);
+ module_put(owner);
  return -ENODEV;
  }
 
@@ -820,7 +823,9 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
  ret = PTR_ERR(blkg);
  rcu_read_unlock();
  spin_unlock_irq(disk->queue->queue_lock);
+ owner = disk->fops->owner;
  put_disk(disk);
+ module_put(owner);
  /*
  * If queue was bypassing, we should retry.  Do so after a
  * short msleep().  It isn't strictly necessary but queue
@@ -851,9 +856,13 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep);
 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
  __releases(ctx->disk->queue->queue_lock) __releases(rcu)
 {
+ struct module *owner;
+
  spin_unlock_irq(ctx->disk->queue->queue_lock);
  rcu_read_unlock();
+ owner = ctx->disk->fops->owner;
  put_disk(ctx->disk);
+ module_put(owner);
 }
 EXPORT_SYMBOL_GPL(blkg_conf_finish);
 
--
2.7.4


--
kernel-team mailing list
[hidden email]
https://lists.ubuntu.com/mailman/listinfo/kernel-team
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

ACK: [SRU][Xenial][PATCH 0/1] block: fix module reference leak on put_disk() call for cgroups throttle

Kamal Mostafa-2
In reply to this post by Joseph Salisbury-3
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

ACK: [SRU][Xenial][PATCH 0/1] block: fix module reference leak on put_disk() call for cgroups throttle

Colin Ian King-2
In reply to this post by Joseph Salisbury-3
On 19/04/17 19:33, Joseph Salisbury wrote:

> BugLink: http://bugs.launchpad.net/bugs/1683976
>
> == SRU Justification ==
> Due to this bug, the module reference count will leak whenever you write to
> /sys/fs/cgroup/blkio/blkio.throttle.*  There is a script in the bug report
> to reproduce the bug.
>
> Commit 39a169b62b41 resolves this bug and was added to mainline in
> v4.5-rc5.  However, it was not cc'd to stable.
>
> This commit is also needed in Trusty, but needs a minor backport.  The Trusty
> SRU will be sent separately.
>
> == Fix ==
> commit 39a169b62b415390398291080dafe63aec751e0a
> Author: Roman Pen <[hidden email]>
> Date:   Tue Feb 9 12:33:35 2016 -0700
>
>     block: fix module reference leak on put_disk() call for cgroups throttle
>
> == Test Case ==
> A test kernel was built with this patch and tested by the original bug reporter.
> The bug reporter states the test kernel resolved the bug.
>
>
> Roman Pen (1):
>   block: fix module reference leak on put_disk() call for cgroups
>     throttle
>
>  block/blk-cgroup.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
Sane looking upstream fix, backport looks good, good test case and good
test results for Xenial.

Thanks Joe.

Acked-by: Colin Ian King <[hidden email]>

--
kernel-team mailing list
[hidden email]
https://lists.ubuntu.com/mailman/listinfo/kernel-team
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

APPLIED: [SRU][Xenial][PATCH 0/1] block: fix module reference leak on put_disk() call for cgroups throttle

Thadeu Lima de Souza Cascardo-3
In reply to this post by Joseph Salisbury-3
Applied to xenial master-next branch.

Thanks.
Cascardo.

--
kernel-team mailing list
[hidden email]
https://lists.ubuntu.com/mailman/listinfo/kernel-team
Loading...