lkml.org 
[lkml]   [2009]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [tip:tracing/urgent] tracing: Fix too large stack usage in do_one_initcall()
    From
    Date
    On Fri, 2009-08-21 at 13:14 +0200, Ingo Molnar wrote:

    > > There's a lot of fat functions on that stack trace, but
    > > the largest of all is do_one_initcall(). This is due to
    > > the boot trace entry variables being on the stack.
    > >
    > > Fixing this is relatively easy, initcalls are fundamentally
    > > serialized, so we can move the local variables to file scope.
    > >
    > > Note that this large stack footprint was present for a
    > > couple of months already - what pushed my system over
    > > the edge was the addition of kmemleak to the call-chain:
    > >
    > > 6) 3328 36 allocate_slab+0xb1/0x100
    > > 7) 3292 36 new_slab+0x1c/0x160
    > > 8) 3256 36 __slab_alloc+0x133/0x2b0
    > > 9) 3220 4 kmem_cache_alloc+0x1bb/0x1d0
    > > 10) 3216 108 create_object+0x28/0x250
    > > 11) 3108 40 kmemleak_alloc+0x81/0xc0
    > > 12) 3068 24 kmem_cache_alloc+0x162/0x1d0
    > > 13) 3044 52 scsi_pool_alloc_command+0x29/0x70
    > >
    > > This pushes the total to ~3800 bytes, only a tiny bit
    > > more was needed to corrupt the on-kernel-stack thread_info.
    > >
    > > The fix reduces the stack footprint from 572 bytes
    > > to 28 bytes.
    >
    > btw., it will just take two more features like kmemleak to trigger
    > hard to debug stack overflows again on 32-bit. We are right at the
    > edge and this situation is not really fixable in a reliable way
    > anymore.
    >
    > So i think we should be more drastic and solve the real problem: we
    > should drop 4K stacks and 8K combo-stacks on 32-bit, and go
    > exclusively to 8K split stacks on 32-bit.
    >
    > I.e. the stack size will be 'unified' too between 64-bit and 32-bit
    > to a certain degree: process stacks will be 8K on both 64-bit and
    > 32-bit x86, IRQ stacks will be separate. (on 64-bit we also have the
    > IST stacks for certain exceptions that further isolates things)
    >
    > This will simplify the 32-bit situation quite a bit and removes a
    > contentious config option and makes the kernel more robust in
    > general. 8K combo stacks are not safe due to irq nesting and 4K
    > isolated stacks are not enough. 8K isolated stacks is the way to go.
    >
    > Opinions?

    I'm obviously all in favour of merging the i386 and x86_64 stack code.
    Esp after having had to look at the i386 stuff recently.

    Now I don't think that unifying all this requires the sizes to be the
    same between them, because x86_64 typically has larger stack footprint
    due to it being 64 bit. If we need to bump 32 bit stack sizes, then
    we're likely to also need a bump in 64 bit as well at some point soon.




    \
     
     \ /
      Last update: 2009-08-21 13:41    [W:2.815 / U:0.040 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site