[lkml]   [2012]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Boot failure since 3.3-rc?
    Incidentally, I had to swap a wifi card, and bisecting now leads to a 
    different bad commit(?)

    This is what it says is the culprit now (I wonder if I should bisect
    again, and attempt booting maybe 3 or 4 times each time):

    f94edacf998516ac9d849f7bc6949a703977a7f3 is the first bad commit
    commit f94edacf998516ac9d849f7bc6949a703977a7f3
    Author: Linus Torvalds <>
    Date: Fri Feb 17 21:48:54 2012 -0800

    i387: move TS_USEDFPU flag from thread_info to task_struct

    This moves the bit that indicates whether a thread has ownership of the
    FPU from the TS_USEDFPU bit in thread_info->status to a word of its own
    (called 'has_fpu') in task_struct->thread.has_fpu.

    This fixes two independent bugs at the same time:

    - changing 'thread_info->status' from the scheduler causes nasty
    problems for the other users of that variable, since it is
    defined to
    be thread-synchronous (that's what the "TS_" part of the naming was
    supposed to indicate).

    So perfectly valid code could (and did) do

    ti->status |= TS_RESTORE_SIGMASK;

    and the compiler was free to do that as separate load, or and store
    instructions. Which can cause problems with preemption, since a
    switch could happen in between, and change the TS_USEDFPU bit. The
    change to TS_USEDFPU would be overwritten by the final store.

    In practice, this seldom happened, though, because the 'status'
    was seldom used more than once, so gcc would generally tend to
    generate code that used a read-modify-write instruction and thus
    happened to avoid this problem - RMW instructions are naturally low
    fat and preemption-safe.

    - On x86-32, the current_thread_info() pointer would, during
    and softirqs, point to a *copy* of the real thread_info, because
    x86-32 uses %esp to calculate the thread_info address, and thus the
    separate irq (and softirq) stacks would cause these kinds of odd
    thread_info copy aliases.

    This is normally not a problem, since interrupts aren't supposed to
    look at thread information anyway (what thread is running at
    interrupt time really isn't very well-defined), but it confused the
    heck out of irq_fpu_usable() and the code that tried to squirrel
    away the FPU state.

    (It also caused untold confusion for us poor kernel developers).

    It also turns out that using 'task_struct' is actually much more
    for most of the call sites that care about the FPU state, since they
    tend to work with the task struct for other reasons anyway (ie
    scheduling). And the FPU data that we are going to save/restore is
    found there too.

    Thanks to Arjan Van De Ven <> for pointing us to
    the %esp issue.

    Cc: Arjan van de Ven <>
    Reported-and-tested-by: Raphael Prevost <>
    Acked-and-tested-by: Suresh Siddha <>
    Tested-by: Peter Anvin <>
    Signed-off-by: Linus Torvalds <>

    :040000 040000 19548f49884c9745ecb3970321ff41b244d79b97
    ec8b1a02dd7ef354f1be4c68767e4353819dd5fa M arch

    For obvious reasons, this commit cannot be easily reverted, but help is
    much appreciated!


    Unix is not an 'a-ha' experience, it is more of a 'holy-shit' experience.
    - Colin McFadyen

     \ /
      Last update: 2012-05-03 19:41    [W:0.025 / U:4.380 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site