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)
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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
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