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    Subjectpstore dump inside an nmi handler
    Hi Tony,

    I was playing with the APEI EINJ module, injecting errors trying to
    capture a GHES record, then panic into a kdump kernel and reboot.

    Matthew brought to my attention that pstore should capture an error record
    on the panic path using kmsg_dump(). After injecting an error with EINJ,
    I went to check to see if there was a pstore entry. There wasn't.

    Playing on another box, I noticed the machine double faulted and didn't
    even make it into a kdump kernel.

    Upon investigation, I noticed that when a fatal error occurs on the
    platform, it will generate an NMI that will be handle by the
    ghes_nmi_handler. This handler calls panic() which calls kmsg_dump()
    which calls pstore_dump().

    Inside pstore_dump(), the first thing it tries to grab is a mutex_lock()
    (inside an nmi hander). This seems to be the root cause of my problems.

    I am not familiar enough with pstore to just modify its locking, so I
    wanted to ask you.

    My first thought was to wrap the mutex_lock with a 'if !in_nmi()', but that
    seemed kinda hacky. Then I was wondering if there was a way to do this
    locklessly or atomically because you are only dealing with whole blocks I
    think. I don't know.

    Wanted to give you a heads up and seek your thoughts. I am willing to
    hack up some code and test. :-)


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      Last update: 2011-07-08 22:19    [W:0.022 / U:102.744 seconds]
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