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https://github.com/riscv-software-src/opensbi.git
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lib: sbi_init: Avoid thundering hurd problem with coldboot_lock
We can have thundering hurd problem with coldboot_lock where the boot HART can potentially starve trying to acquire coldboot_lock because some of the non-boot HARTs are continuously acquiring and releasing coldboot_lock. This can happen if MIP.MSIP bit is already set for some of the non-boot HARTs. To avoid thundering hurd problem for coldboot_lock, we use the __smp_load_acquire() and __smp_store_release() for coldboot_done flag and use coldboot_lock only for coldboot_wait_hmask. Signed-off-by: Anup Patel <anup.patel@wdc.com> Tested-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Reviewed-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Bin Meng <bin.meng@windriver.com>
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@@ -9,6 +9,7 @@
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#include <sbi/riscv_asm.h>
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#include <sbi/riscv_atomic.h>
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#include <sbi/riscv_barrier.h>
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#include <sbi/riscv_locks.h>
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#include <sbi/sbi_console.h>
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#include <sbi/sbi_ecall.h>
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@@ -85,9 +86,10 @@ static void sbi_boot_prints(struct sbi_scratch *scratch, u32 hartid)
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}
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static spinlock_t coldboot_lock = SPIN_LOCK_INITIALIZER;
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static unsigned long coldboot_done = 0;
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static struct sbi_hartmask coldboot_wait_hmask = { 0 };
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static unsigned long coldboot_done;
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static void wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
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{
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unsigned long saved_mie, cmip;
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@@ -105,16 +107,20 @@ static void wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
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/* Mark current HART as waiting */
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sbi_hartmask_set_hart(hartid, &coldboot_wait_hmask);
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/* Release coldboot lock */
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spin_unlock(&coldboot_lock);
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/* Wait for coldboot to finish using WFI */
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while (!coldboot_done) {
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spin_unlock(&coldboot_lock);
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while (!__smp_load_acquire(&coldboot_done)) {
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do {
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wfi();
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cmip = csr_read(CSR_MIP);
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} while (!(cmip & MIP_MSIP));
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spin_lock(&coldboot_lock);
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};
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/* Acquire coldboot lock */
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spin_lock(&coldboot_lock);
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/* Unmark current HART as waiting */
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sbi_hartmask_clear_hart(hartid, &coldboot_wait_hmask);
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@@ -132,12 +138,12 @@ static void wake_coldboot_harts(struct sbi_scratch *scratch, u32 hartid)
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{
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const struct sbi_platform *plat = sbi_platform_ptr(scratch);
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/* Mark coldboot done */
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__smp_store_release(&coldboot_done, 1);
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/* Acquire coldboot lock */
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spin_lock(&coldboot_lock);
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/* Mark coldboot done */
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coldboot_done = 1;
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/* Send an IPI to all HARTs waiting for coldboot */
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for (int i = 0; i <= sbi_scratch_last_hartid(); i++) {
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if ((i != hartid) &&
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