• Tejun Heo's avatar
    dump_stack: consolidate dump_stack() implementations and unify their behaviors · 196779b9
    Tejun Heo authored
    Both dump_stack() and show_stack() are currently implemented by each
    architecture.  show_stack(NULL, NULL) dumps the backtrace for the
    current task as does dump_stack().  On some archs, dump_stack() prints
    extra information - pid, utsname and so on - in addition to the
    backtrace while the two are identical on other archs.
    The usages in arch-independent code of the two functions indicate
    show_stack(NULL, NULL) should print out bare backtrace while
    dump_stack() is used for debugging purposes when something went wrong,
    so it does make sense to print additional information on the task which
    triggered dump_stack().
    There's no reason to require archs to implement two separate but mostly
    identical functions.  It leads to unnecessary subtle information.
    This patch expands the dummy fallback dump_stack() implementation in
    lib/dump_stack.c such that it prints out debug information (taken from
    x86) and invokes show_stack(NULL, NULL) and drops arch-specific
    dump_stack() implementations in all archs except blackfin.  Blackfin's
    dump_stack() does something wonky that I don't understand.
    Debug information can be printed separately by calling
    dump_stack_print_info() so that arch-specific dump_stack()
    implementation can still emit the same debug information.  This is used
    in blackfin.
    This patch brings the following behavior changes.
    * On some archs, an extra level in backtrace for show_stack() could be
      printed.  This is because the top frame was determined in
      dump_stack() on those archs while generic dump_stack() can't do that
      reliably.  It can be compensated by inlining dump_stack() but not
      sure whether that'd be necessary.
    * Most archs didn't use to print debug info on dump_stack().  They do
    An example WARN dump follows.
     WARNING: at kernel/workqueue.c:4841 init_workqueues+0x35/0x505()
     Hardware name: empty
     Modules linked in:
     CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.9.0-rc1-work+ #9
      0000000000000009 ffff88007c861e08 ffffffff81c614dc ffff88007c861e48
      ffffffff8108f50f ffffffff82228240 0000000000000040 ffffffff8234a03c
      0000000000000000 0000000000000000 0000000000000000 ffff88007c861e58
     Call Trace:
      [<ffffffff81c614dc>] dump_stack+0x19/0x1b
      [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0
      [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20
      [<ffffffff8234a071>] init_workqueues+0x35/0x505
    v2: CPU number added to the generic debug info as requested by s390
        folks and dropped the s390 specific dump_stack().  This loses %ksp
        from the debug message which the maintainers think isn't important
        enough to keep the s390-specific dump_stack() implementation.
        dump_stack_print_info() is moved to kernel/printk.c from
        lib/dump_stack.c.  Because linkage is per objecct file,
        dump_stack_print_info() living in the same lib file as generic
        dump_stack() means that archs which implement custom dump_stack()
        - at this point, only blackfin - can't use dump_stack_print_info()
        as that will bring in the generic version of dump_stack() too.  v1
        The v1 patch broke build on blackfin due to this issue.  The build
        breakage was reported by Fengguang Wu.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
    Acked-by: default avatarVineet Gupta <vgupta@synopsys.com>
    Acked-by: default avatarJesper Nilsson <jesper.nilsson@axis.com>
    Acked-by: default avatarVineet Gupta <vgupta@synopsys.com>
    Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>	[s390 bits]
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Mike Frysinger <vapier@gentoo.org>
    Cc: Fengguang Wu <fengguang.wu@intel.com>
    Cc: Bjorn Helgaas <bhelgaas@google.com>
    Cc: Sam Ravnborg <sam@ravnborg.org>
    Acked-by: Richard Kuo <rkuo@codeaurora.org>		[hexagon bits]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>