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SubjectRe: next-20090310: ext4 hangs


Jan Kara wrote:
> Hi,
>
> thanks for the updated disassembly.
>
>> 55bab0: 82 10 60 01 or %g1, 1, %g1
>> spin_unlock(&journal->j_list_lock);
>> 55bab4: 40 06 4b 20 call 6ee734 <_spin_unlock>
>> 55bab8: c2 24 e0 28 st %g1, [ %l3 + 0x28 ]
> OK, so it really seems that:
> jinode->i_flags |= JI_COMMIT_RUNNING;
> spin_unlock(&journal->j_list_lock);
>
> has been compiled to
> ld [ %l3 + 0x28 ], %g1
> or %g1, 1, %g1
> call 6ee734 <_spin_unlock>
> st %g1, [ %l3 + 0x28 ]
>
> Which seems like a bug in the compiler or in the way implement compiler
> barriers in spin_unlock() on UP sparc. Or is there some sparc magic by which
> this is correct code? Any clever sparc guy?
>
> Honza


Looks fine to me - the store is made in the branch delay slot
of the call, so it will occur before the first instruction at
the call target address executes.
Jiri.


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