51a325a7f9
points to the TLS in user space and points to the PCPU structure in the kernel. The race is the result of having the exception handler on the one hand and the RPC system call entry on the other. The EPC syscall path is non-atomic in that interrupts are enabled while the two stacks are switched. The register stack is switched last as that is the stack used to determine whether we're going back to user space by the exception handler. If we go back to user space, we restore r13, otherwise we leave r13 alone. The EPC syscall path however set r13 to the PCPU structure *before* switching the register stack, which means that there was a window in which the exception handler would restore r13 when it was already pointing to the PCPU structure. This is fatal when the exception happened on CPU x, but left from the exception on anotehr CPU. In that case r13 would point to the PCPU of the CPU the thread was running on. This immediately results in getting the wrong value for curthread. The fix is to make sure we assign r13 *after* we set ar.bspstore to point to the kernel register stack for the thread. |
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| .. | ||
| acpica | ||
| compile | ||
| conf | ||
| disasm | ||
| ia32 | ||
| ia64 | ||
| include | ||
| isa | ||
| pci | ||