From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- drivers/scsi/scsi_debugfs.c | 75 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 drivers/scsi/scsi_debugfs.c (limited to 'drivers/scsi/scsi_debugfs.c') diff --git a/drivers/scsi/scsi_debugfs.c b/drivers/scsi/scsi_debugfs.c new file mode 100644 index 000000000..eb52e39f3 --- /dev/null +++ b/drivers/scsi/scsi_debugfs.c @@ -0,0 +1,75 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include "scsi_debugfs.h" + +#define SCSI_CMD_FLAG_NAME(name)[const_ilog2(SCMD_##name)] = #name +static const char *const scsi_cmd_flags[] = { + SCSI_CMD_FLAG_NAME(TAGGED), + SCSI_CMD_FLAG_NAME(INITIALIZED), + SCSI_CMD_FLAG_NAME(LAST), +}; +#undef SCSI_CMD_FLAG_NAME + +static int scsi_flags_show(struct seq_file *m, const unsigned long flags, + const char *const *flag_name, int flag_name_count) +{ + bool sep = false; + int i; + + for_each_set_bit(i, &flags, BITS_PER_LONG) { + if (sep) + seq_puts(m, "|"); + sep = true; + if (i < flag_name_count && flag_name[i]) + seq_puts(m, flag_name[i]); + else + seq_printf(m, "%d", i); + } + return 0; +} + +static const char *scsi_cmd_list_info(struct scsi_cmnd *cmd) +{ + struct Scsi_Host *shost = cmd->device->host; + struct scsi_cmnd *cmd2; + + guard(spinlock_irq)(shost->host_lock); + + list_for_each_entry(cmd2, &shost->eh_abort_list, eh_entry) + if (cmd == cmd2) + return "on eh_abort_list"; + + list_for_each_entry(cmd2, &shost->eh_cmd_q, eh_entry) + if (cmd == cmd2) + return "on eh_cmd_q"; + + return NULL; +} + +void scsi_show_rq(struct seq_file *m, struct request *rq) +{ + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq); + int alloc_ms = jiffies_to_msecs(jiffies - cmd->jiffies_at_alloc); + int timeout_ms = jiffies_to_msecs(rq->timeout); + char buf[80] = "(?)"; + + if (cmd->flags & SCMD_INITIALIZED) { + const char *list_info = scsi_cmd_list_info(cmd); + + __scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len); + seq_printf(m, ", .cmd=%s, .retries=%d, .allowed=%d, .result = %#x%s%s", + buf, cmd->retries, cmd->allowed, cmd->result, + list_info ? ", " : "", list_info ? : ""); + seq_printf(m, ", .timeout=%d.%03d, allocated %d.%03d s ago", + timeout_ms / 1000, timeout_ms % 1000, + alloc_ms / 1000, alloc_ms % 1000); + } + seq_printf(m, ", .flags="); + scsi_flags_show(m, cmd->flags, scsi_cmd_flags, + ARRAY_SIZE(scsi_cmd_flags)); +} -- cgit v1.3.1