On 4/16/23 22:33, Andrew Morton wrote:
Circling back to this fix... The BUG() is obviously real. We're unsure that Ivan's fix is the best one. We haven't identified a Fixes:, and as this report is against the 6.2 kernel, a cc:stable will be needed. According to the sysbot bisection (https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959fc), this is present in linux-5.19, so it might predate Zach's 58ac9a8993a13ebc changes. But that bisection claim might be misleading. And Zach is offline for a few months. So can people please take a look and see if we can get this wrapped up? Matthew, the assertion failure is in the VM_BUG_ON(index != xas.xa_index); which was added in 77da9389b9d5f, so perhaps you could take a look? Thanks.
I tested the reproducers on the 99cb0dbd47a15 commit, and they do not trigger the problematic condition of shared memory truncation or hole-punching. I will investigate further, as there have been many changes in khugepaged since the 99cb0dbd47a15 commit that could potentially affect its behavior.
