Re: Patch "coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping" has been added to the 4.4-stable tree
On Tue, Jun 04, 2019 at 04:52:31PM +0200, Michal Hocko wrote:
Please note that I have posted my backport today http://lkml.kernel.org/r/20190604094953.26688-1-mhocko@kernel.org and it differs from this one. Please have a look!
Ah, good point, I just noticed that. Ben, any thoughts as to the difference?
thanks,
greg k-h
On Tue, 2019-06-04 at 17:07 +0200, Greg KH wrote:
On Tue, Jun 04, 2019 at 04:52:31PM +0200, Michal Hocko wrote:
Please note that I have posted my backport today http://lkml.kernel.org/r/20190604094953.26688-1-mhocko@kernel.org and it differs from this one. Please have a look!
Ah, good point, I just noticed that. Ben, any thoughts as to the difference?
- The additional fix in binder makes sense to me, and is also needed in 4.9. I'm not sure why I missed it.
- I don't understand why collapse_huge_range() needs to be fixed, but then I really don't understand the khugepaged code at all! So I would trust Michal on this.
- The userfaultfd fixes look different because I picked "userfaultfd: don't pin the user memory in userfaultfd_file_create()" first and Michal did not. I don't think it makes sense to be calling mmget_still_valid() in these functions if they don't use mmget_not_zero() or similar. But again, Michal is the expert here.
Ben.
On Tue 04-06-19 16:51:38, Ben Hutchings wrote: [...]
- I don't understand why collapse_huge_range() needs to be fixed, but
then I really don't understand the khugepaged code at all! So I would trust Michal on this.
To be honest, I am not really sure myself here. But we are using a remote mm there and I do not see anything that would prevent from racing with exit/coredump. Maybe I am wrong. Let's wait for Andrea for his review feedback. This patch is quite tricky for the stable backport.
Thanks!
On Wed, 2019-06-05 at 08:50 +0200, Michal Hocko wrote:
On Tue 04-06-19 16:51:38, Ben Hutchings wrote: [...]
- I don't understand why collapse_huge_range() needs to be fixed, but
then I really don't understand the khugepaged code at all! So I would trust Michal on this.
To be honest, I am not really sure myself here. But we are using a remote mm there and I do not see anything that would prevent from racing with exit/coredump. Maybe I am wrong. Let's wait for Andrea for his review feedback. This patch is quite tricky for the stable backport.
So, Greg, it seems like you should drop this from the current stable round.
Ben.
On Wed, Jun 05, 2019 at 01:08:48PM +0100, Ben Hutchings wrote:
On Wed, 2019-06-05 at 08:50 +0200, Michal Hocko wrote:
On Tue 04-06-19 16:51:38, Ben Hutchings wrote: [...]
- I don't understand why collapse_huge_range() needs to be fixed, but
then I really don't understand the khugepaged code at all! So I would trust Michal on this.
To be honest, I am not really sure myself here. But we are using a remote mm there and I do not see anything that would prevent from racing with exit/coredump. Maybe I am wrong. Let's wait for Andrea for his review feedback. This patch is quite tricky for the stable backport.
So, Greg, it seems like you should drop this from the current stable round.
Ok, will do, thanks.
greg k-h
linux-stable-mirror@lists.linaro.org
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Ben Hutchings -
Greg KH -
Michal Hocko