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Implement rtas_call_reentrant() for reentrant rtas-calls: "ibm,int-on", "ibm,int-off",ibm,get-xive" and "ibm,set-xive". On LoPAPR Version 1.1 (March 24, 2016), from 7.3.10.1 to 7.3.10.4, items 2 and 3 say: 2 - For the PowerPC External Interrupt option: The * call must be reentrant to the number of processors on the platform. 3 - For the PowerPC External Interrupt option: The * argument call buffer for each simultaneous call must be physically unique. So, these rtas-calls can be called in a lockless way, if using a different buffer for each cpu doing such rtas call. For this, it was suggested to add the buffer (struct rtas_args) in the PACA struct, so each cpu can have it's own buffer. The PACA struct received a pointer to rtas buffer, which is allocated in the memory range available to rtas 32-bit. Reentrant rtas calls are useful to avoid deadlocks in crashing, where rtas-calls are needed, but some other thread crashed holding the rtas.lock. This is a backtrace of a deadlock from a kdump testing environment: #0 arch_spin_lock #1 lock_rtas () #2 rtas_call (token=8204, nargs=1, nret=1, outputs=0x0) #3 ics_rtas_mask_real_irq (hw_irq=4100) #4 machine_kexec_mask_interrupts #5 default_machine_crash_shutdown #6 machine_crash_shutdown #7 __crash_kexec #8 crash_kexec #9 oops_end Signed-off-by: Leonardo Bras <leobras.c@gmail.com> [mpe: Move under #ifdef PSERIES to avoid build breakage] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200518234245.200672-3-leobras.c@gmail.com |
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