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Patch "coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping" has been added to the 4.4-stable tree

DISCUSSION Greg KH 3 participants 5 messages Jun 4, 2019 – Jun 6, 2019 2 messages not in the archive Stable branch

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#3 lore raw
Quoted 7 lines · Greg KH
Quoted 3 lines · Michal Hocko

Please note that I have posted my backport today
http://lkml.kernel.org/r/[email protected] 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.

Signature · 3 lines
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom
#4 lore raw

On Tue 04-06-19 16:51:38, Ben Hutchings wrote:
[...]

Quoted 3 lines

- 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!

Signature · 2 lines
Michal Hocko
SUSE Labs
#5 lore raw
Quoted 10 lines · Michal Hocko

On Tue 04-06-19 16:51:38, Ben Hutchings wrote:
[...]

Quoted 3 lines

- 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.

Signature · 3 lines
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom
author maintainer
#6 lore raw
Quoted 7 lines · Ben Hutchings
Quoted 6 lines · Michal Hocko

On Tue 04-06-19 16:51:38, Ben Hutchings wrote:
[...]

Quoted 3 lines

- 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.

Quoted 7 lines
Quoted 4 lines

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