mirror of https://gitee.com/openkylin/linux.git
b32aadc1a8
core_idle_state is maintained for each core. It uses 0-7 bits to track whether a thread in the core has entered fastsleep or winkle. 8th bit is used as a lock bit. The lock bit is set in these 2 scenarios- - The thread is first in subcore to wakeup from sleep/winkle. - If its the last thread in the core about to enter sleep/winkle While the lock bit is set, if any other thread in the core wakes up, it loops until the lock bit is cleared before proceeding in the wakeup path. This helps prevent race conditions w.r.t fastsleep workaround and prevents threads from switching to process context before core/subcore resources are restored. But, in the path to sleep/winkle entry, we currently don't check for lock-bit. This exposes us to following race when running with subcore on- First thread in the subcorea Another thread in the same waking up core entering sleep/winkle lwarx r15,0,r14 ori r15,r15,PNV_CORE_IDLE_LOCK_BIT stwcx. r15,0,r14 [Code to restore subcore state] lwarx r15,0,r14 [clear thread bit] stwcx. r15,0,r14 andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS stw r15,0(r14) Here, after the thread entering sleep clears its thread bit in core_idle_state, the value is overwritten by the thread waking up. In such cases when the core enters fastsleep, code mistakes an idle thread as running. Because of this, the first thread waking up from fastsleep which is supposed to resync timebase skips it. So we can end up having a core with stale timebase value. This patch fixes the above race by looping on the lock bit even while entering the idle states. Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> Fixes: 7b54e9f213f76 'powernv/powerpc: Add winkle support for offline cpus' Cc: stable@vger.kernel.org # 3.19+ Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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