Public bug reported:

[Impact]

The option CONFIG_DMA_CMA seems to cause resume problems on the t2.*
instance types (Xen).

With this option enabled device drivers are allowed to use the Contiguous 
Memory Allocator (CMA) for DMA operations. So, drivers can allocate large 
physically-contiguous blocks of memory, instead of relying on the I/O map or 
scatter-gather support.
    
However, on resume, the memory used by DMA needs to be re-initialized / 
re-allocated, but it may fail to allocate large chunks of contiguous memory due 
to the fact that we also need to restore the hibernation image, using more 
memory and causing a system hang during the resume process.

[Test case]

Hibernate / resume any t2.* instance (especially t2.nano, where the
problem seems to happen 100% of the times after 2 consecutive
hibernate/resume cycles).

[Fix]

Disable CONFIG_DMA_CMA.

NOTE: this option is already disabled in the generic kernel (see LP:
#1362261).

[Regression potential]

It is a .config change, no regression potential except with the fact
that disabling this option also disables the module 'etnaviv' (Vivante
graphic card), that is not really needed in the aws kernel.

** Affects: linux-aws (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: linux-aws (Ubuntu Focal)
     Importance: High
     Assignee: Andrea Righi (arighi)
         Status: New

** Also affects: linux (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Package changed: linux (Ubuntu) => linux-aws (Ubuntu)

** Changed in: linux-aws (Ubuntu Focal)
   Importance: Undecided => High

** Changed in: linux-aws (Ubuntu Focal)
     Assignee: (unassigned) => Andrea Righi (arighi)

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1879711

Title:
  aws: disable CONFIG_DMA_CMA

Status in linux-aws package in Ubuntu:
  New
Status in linux-aws source package in Focal:
  New

Bug description:
  [Impact]

  The option CONFIG_DMA_CMA seems to cause resume problems on the t2.*
  instance types (Xen).

  With this option enabled device drivers are allowed to use the Contiguous 
Memory Allocator (CMA) for DMA operations. So, drivers can allocate large 
physically-contiguous blocks of memory, instead of relying on the I/O map or 
scatter-gather support.
      
  However, on resume, the memory used by DMA needs to be re-initialized / 
re-allocated, but it may fail to allocate large chunks of contiguous memory due 
to the fact that we also need to restore the hibernation image, using more 
memory and causing a system hang during the resume process.

  [Test case]

  Hibernate / resume any t2.* instance (especially t2.nano, where the
  problem seems to happen 100% of the times after 2 consecutive
  hibernate/resume cycles).

  [Fix]

  Disable CONFIG_DMA_CMA.

  NOTE: this option is already disabled in the generic kernel (see LP:
  #1362261).

  [Regression potential]

  It is a .config change, no regression potential except with the fact
  that disabling this option also disables the module 'etnaviv' (Vivante
  graphic card), that is not really needed in the aws kernel.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux-aws/+bug/1879711/+subscriptions

-- 
Mailing list: https://launchpad.net/~kernel-packages
Post to     : kernel-packages@lists.launchpad.net
Unsubscribe : https://launchpad.net/~kernel-packages
More help   : https://help.launchpad.net/ListHelp

Reply via email to