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. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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