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lib: sbi_init: Avoid thundering hurd problem with coldboot_lock

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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>
This commit is contained in:
Anup Patel
2020-08-15 19:41:11 +05:30
committed by Anup Patel
parent d7f87d99a3
commit e435ba0524
1 changed files with 13 additions and 7 deletions
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20
lib/sbi/sbi_init.c
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@@ -9,6 +9,7 @@
#include <sbi/riscv_asm.h>
#include <sbi/riscv_atomic.h>
#include <sbi/riscv_barrier.h>
#include <sbi/riscv_locks.h>
#include <sbi/sbi_console.h>
#include <sbi/sbi_ecall.h>
@@ -85,9 +86,10 @@ static void sbi_boot_prints(struct sbi_scratch *scratch, u32 hartid)
}
static spinlock_t coldboot_lock = SPIN_LOCK_INITIALIZER;
static unsigned long coldboot_done = 0;
static struct sbi_hartmask coldboot_wait_hmask = { 0 };
static unsigned long coldboot_done;
static void wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
{
unsigned long saved_mie, cmip;
@@ -105,16 +107,20 @@ static void wait_for_coldboot(struct sbi_scratch *scratch, u32 hartid)
/* Mark current HART as waiting */
sbi_hartmask_set_hart(hartid, &coldboot_wait_hmask);
/* Release coldboot lock */
spin_unlock(&coldboot_lock);
/* Wait for coldboot to finish using WFI */
while (!coldboot_done) {
spin_unlock(&coldboot_lock);
while (!__smp_load_acquire(&coldboot_done)) {
do {
wfi();
cmip = csr_read(CSR_MIP);
} while (!(cmip & MIP_MSIP));
spin_lock(&coldboot_lock);
};
/* Acquire coldboot lock */
spin_lock(&coldboot_lock);
/* Unmark current HART as waiting */
sbi_hartmask_clear_hart(hartid, &coldboot_wait_hmask);
@@ -132,12 +138,12 @@ static void wake_coldboot_harts(struct sbi_scratch *scratch, u32 hartid)
{
const struct sbi_platform *plat = sbi_platform_ptr(scratch);
/* Mark coldboot done */
__smp_store_release(&coldboot_done, 1);
/* 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 <= sbi_scratch_last_hartid(); i++) {
if ((i != hartid) &&