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    cpufreq: Initialize governor for a new policy under policy->rwsem · 4e97b631
    Viresh Kumar 提交于
    policy->rwsem is used to lock access to all parts of code modifying
    struct cpufreq_policy, but it's not used on a new policy created by
    __cpufreq_add_dev().
    
    Because of that, if cpufreq_update_policy() is called in a tight loop
    on one CPU in parallel with offline/online of another CPU, then the
    following crash can be triggered:
    
    Unable to handle kernel NULL pointer dereference at virtual address 00000020
    pgd = c0003000
    [00000020] *pgd=80000000004003, *pmd=00000000
    Internal error: Oops: 206 [#1] PREEMPT SMP ARM
    
    PC is at __cpufreq_governor+0x10/0x1ac
    LR is at cpufreq_update_policy+0x114/0x150
    
    ---[ end trace f23a8defea6cd706 ]---
    Kernel panic - not syncing: Fatal exception
    CPU0: stopping
    CPU: 0 PID: 7136 Comm: mpdecision Tainted: G      D W    3.10.0-gd727407-00074-g979ede8 #396
    
    [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58)
    [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) from [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c)
    [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) from [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8)
    [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) from [<c0803e7c>] (cpufreq_init_policy+0x30/0x98)
    [<c0803e7c>] (cpufreq_init_policy+0x30/0x98) from [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4)
    [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) from [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84)
    [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) from [<c0afe180>] (notifier_call_chain+0x40/0x68)
    [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02812dc>] (__cpu_notify+0x28/0x44)
    [<c02812dc>] (__cpu_notify+0x28/0x44) from [<c0aeed90>] (_cpu_up+0xf4/0x1dc)
    [<c0aeed90>] (_cpu_up+0xf4/0x1dc) from [<c0aeeed4>] (cpu_up+0x5c/0x78)
    [<c0aeeed4>] (cpu_up+0x5c/0x78) from [<c0aec808>] (store_online+0x44/0x74)
    [<c0aec808>] (store_online+0x44/0x74) from [<c03a40f4>] (sysfs_write_file+0x108/0x14c)
    [<c03a40f4>] (sysfs_write_file+0x108/0x14c) from [<c03517d4>] (vfs_write+0xd0/0x180)
    [<c03517d4>] (vfs_write+0xd0/0x180) from [<c0351ca8>] (SyS_write+0x38/0x68)
    [<c0351ca8>] (SyS_write+0x38/0x68) from [<c0205de0>] (ret_fast_syscall+0x0/0x30)
    
    Fix that by taking locks at appropriate places in __cpufreq_add_dev()
    as well.
    Reported-by: NSaravana Kannan <skannan@codeaurora.org>
    Suggested-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
    [rjw: Changelog]
    Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
    4e97b631
cpufreq.c 60.7 KB