From e561c6303639ed510183da25d3d54555a53371c9 Mon Sep 17 00:00:00 2001
From: Anup Patel <anup.patel@wdc.com>
Date: Thu, 26 Sep 2019 09:55:25 +0530
Subject: lib: Fix coldboot race condition observed on emulators/simulators
If we are running on RISC-V emulator/simulator with large number of
HARTs where each HART is a regular thread under UNIX host then it is
possible that some of the secondary HARTs don't get chance to run and
sbi_hart_wake_coldboot_harts() is called before secondary HARTs call
sbi_hart_wait_for_coldboot(). In this situation, some of the secondary
HARTs will never come-out of coldboot wait loop.
To tackle this, we introduce a global flag coldboot_done which will
be protected by coldboot lock and it will be set by primary HART from
sbi_hart_wake_coldboot_harts() before waking-up secondary HARTs. We
also re-arrange acquire/release of coldboot lock to reduce further
chances of race-condition.
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Nylon Chen<nylon7@andestech.com>
---
lib/sbi/sbi_hart.c | 44 +++++++++++++++++++++++++++++---------------
1 file changed, 29 insertions(+), 15 deletions(-)
diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
index b0c087a..dee2e21 100644
--- a/lib/sbi/sbi_hart.c
+++ b/lib/sbi/sbi_hart.c
@@ -344,12 +344,12 @@ struct sbi_scratch *sbi_hart_id_to_scratch(struct sbi_scratch *scratch,
}
#define COLDBOOT_WAIT_BITMAP_SIZE __riscv_xlen
-static spinlock_t coldboot_wait_bitmap_lock = SPIN_LOCK_INITIALIZER;
-static unsigned long coldboot_wait_bitmap = 0;
+static spinlock_t coldboot_lock = SPIN_LOCK_INITIALIZER;
+static unsigned long coldboot_done = 0;
+static unsigned long coldboot_wait_bitmap = 0;
void sbi_hart_wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
{
- unsigned long mipval;
const struct sbi_platform *plat = sbi_platform_ptr(scratch);
if ((sbi_platform_hart_count(plat) <= hartid) ||
@@ -359,19 +359,26 @@ void sbi_hart_wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
/* Set MSIE bit to receive IPI */
csr_set(CSR_MIE, MIP_MSIP);
- do {
- spin_lock(&coldboot_wait_bitmap_lock);
- coldboot_wait_bitmap |= (1UL << hartid);
- spin_unlock(&coldboot_wait_bitmap_lock);
+ /* Acquire coldboot lock */
+ spin_lock(&coldboot_lock);
+ /* Mark current HART as waiting */
+ coldboot_wait_bitmap |= (1UL << hartid);
+
+ /* Wait for coldboot to finish using WFI */
+ while (!coldboot_done) {
+ spin_unlock(&coldboot_lock);
wfi();
- mipval = csr_read(CSR_MIP);
+ spin_lock(&coldboot_lock);
+ };
+
+ /* Unmark current HART as waiting */
+ coldboot_wait_bitmap &= ~(1UL << hartid);
- spin_lock(&coldboot_wait_bitmap_lock);
- coldboot_wait_bitmap &= ~(1UL << hartid);
- spin_unlock(&coldboot_wait_bitmap_lock);
- } while (!(mipval & MIP_MSIP));
+ /* Release coldboot lock */
+ spin_unlock(&coldboot_lock);
+ /* Clear current HART IPI */
sbi_platform_ipi_clear(plat, hartid);
}
@@ -380,11 +387,18 @@ void sbi_hart_wake_coldboot_harts(struct sbi_scratch *scratch, u32 hartid)
const struct sbi_platform *plat = sbi_platform_ptr(scratch);
int max_hart = sbi_platform_hart_count(plat);
+ /* Acquire coldboot lock */
+ spin_lock(&coldboot_lock);
+
+ /* Mark coldboot done */
+ coldboot_done = 1;
+
+ /* Send an IPI to all HARTs waiting for coldboot */
for (int i = 0; i < max_hart; i++) {
- /* send an IPI to every other hart */
- spin_lock(&coldboot_wait_bitmap_lock);
if ((i != hartid) && (coldboot_wait_bitmap & (1UL << i)))
sbi_platform_ipi_send(plat, i);
- spin_unlock(&coldboot_wait_bitmap_lock);
}
+
+ /* Release coldboot lock */
+ spin_unlock(&coldboot_lock);
}
--
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