• Arve Hjønnevåg's avatar
    PM: Fix suspend_console and resume_console to use only one semaphore · 403f3075
    Arve Hjønnevåg authored
    This fixes a race where a thread acquires the console while the
    console is suspended, and the console is resumed before this
    thread releases it. In this case, the secondary console
    semaphore would be left locked, and the primary semaphore would
    be released twice. This in turn would cause the console switch
    on suspend or resume to hang forever.
    
    Note that suspend_console does not actually lock the console
    for clients that use acquire_console_sem, it only locks it for
    clients that use try_acquire_console_sem. If we change
    suspend_console to fully lock the console, then the kernel
    may deadlock on suspend. One client of try_acquire_console_sem
    is acquire_console_semaphore_for_printk, which uses it to
    prevent printk from using the console while it is suspended.
    Signed-off-by: default avatarArve Hjønnevåg <arve@android.com>
    Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
    Cc: Len Brown <lenb@kernel.org>
    Cc: Greg KH <gregkh@suse.de>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    403f3075
printk.c 31.8 KB