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SubjectRandom shadow stack pointer corruption
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Hi,

My shadow stack tests start to have random shadow stack pointer corruption after
v5.7 (excluding). The symptom looks like some locking issue or the kernel is
confused about which CPU a task is on. In later tip/master, this can be
triggered by creating two tasks and each does continuous
pthread_create()/pthread_join(). If the kernel has max_cpus=1, the issue goes
away. I also checked XSAVES/XRSTORS, but this does not seem to be an issue
coming from there.

The tests I run take a long time to complete, and some commit points in bisect
do not show failures right away. However, the issue can be more easily
triggered after the point of:

d77290507ab2 x86/entry/32: Convert IRET exception to IDTENTRY_SW

Can anyone help me find places to look at?

Thanks,
Yu-cheng

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