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 --- io_uring/filetable.c | 158 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 158 insertions(+) create mode 100644 io_uring/filetable.c (limited to 'io_uring/filetable.c') diff --git a/io_uring/filetable.c b/io_uring/filetable.c new file mode 100644 index 000000000..cb1838c9f --- /dev/null +++ b/io_uring/filetable.c @@ -0,0 +1,158 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "io_uring.h" +#include "rsrc.h" +#include "filetable.h" + +static int io_file_bitmap_get(struct io_ring_ctx *ctx) +{ + struct io_file_table *table = &ctx->file_table; + unsigned long nr = ctx->file_alloc_end; + int ret; + + if (!table->bitmap) + return -ENFILE; + + if (table->alloc_hint < ctx->file_alloc_start || + table->alloc_hint >= ctx->file_alloc_end) + table->alloc_hint = ctx->file_alloc_start; + + do { + ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint); + if (ret != nr) + return ret; + + if (table->alloc_hint == ctx->file_alloc_start) + break; + nr = table->alloc_hint; + table->alloc_hint = ctx->file_alloc_start; + } while (1); + + return -ENFILE; +} + +bool io_alloc_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table, + unsigned nr_files) +{ + if (io_rsrc_data_alloc(&table->data, nr_files)) + return false; + table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT); + if (table->bitmap) + return true; + io_rsrc_data_free(ctx, &table->data); + return false; +} + +void io_free_file_tables(struct io_ring_ctx *ctx, struct io_file_table *table) +{ + io_rsrc_data_free(ctx, &table->data); + bitmap_free(table->bitmap); + table->bitmap = NULL; +} + +static int io_install_fixed_file(struct io_ring_ctx *ctx, struct file *file, + u32 slot_index) + __must_hold(&ctx->uring_lock) +{ + struct io_rsrc_node *node; + + if (io_is_uring_fops(file)) + return -EBADF; + if (!ctx->file_table.data.nr) + return -ENXIO; + if (slot_index >= ctx->file_table.data.nr) + return -EINVAL; + + node = io_rsrc_node_alloc(ctx, IORING_RSRC_FILE); + if (!node) + return -ENOMEM; + + if (!io_reset_rsrc_node(ctx, &ctx->file_table.data, slot_index)) + io_file_bitmap_set(&ctx->file_table, slot_index); + + ctx->file_table.data.nodes[slot_index] = node; + io_fixed_file_set(node, file); + return 0; +} + +int __io_fixed_fd_install(struct io_ring_ctx *ctx, struct file *file, + unsigned int file_slot) +{ + bool alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC; + int ret; + + if (alloc_slot) { + ret = io_file_bitmap_get(ctx); + if (unlikely(ret < 0)) + return ret; + file_slot = ret; + } else { + file_slot--; + } + + ret = io_install_fixed_file(ctx, file, file_slot); + if (!ret && alloc_slot) + ret = file_slot; + return ret; +} +/* + * Note when io_fixed_fd_install() returns error value, it will ensure + * fput() is called correspondingly. + */ +int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags, + struct file *file, unsigned int file_slot) +{ + struct io_ring_ctx *ctx = req->ctx; + int ret; + + io_ring_submit_lock(ctx, issue_flags); + ret = __io_fixed_fd_install(ctx, file, file_slot); + io_ring_submit_unlock(ctx, issue_flags); + + if (unlikely(ret < 0)) + fput(file); + return ret; +} + +int io_fixed_fd_remove(struct io_ring_ctx *ctx, unsigned int offset) +{ + struct io_rsrc_node *node; + + if (unlikely(!ctx->file_table.data.nr)) + return -ENXIO; + if (offset >= ctx->file_table.data.nr) + return -EINVAL; + + node = io_rsrc_node_lookup(&ctx->file_table.data, offset); + if (!node) + return -EBADF; + io_reset_rsrc_node(ctx, &ctx->file_table.data, offset); + io_file_bitmap_clear(&ctx->file_table, offset); + return 0; +} + +int io_register_file_alloc_range(struct io_ring_ctx *ctx, + struct io_uring_file_index_range __user *arg) +{ + struct io_uring_file_index_range range; + u32 end; + + if (copy_from_user(&range, arg, sizeof(range))) + return -EFAULT; + if (check_add_overflow(range.off, range.len, &end)) + return -EOVERFLOW; + if (range.resv || end > ctx->file_table.data.nr) + return -EINVAL; + + io_file_table_set_alloc_range(ctx, range.off, range.len); + return 0; +} -- cgit v1.3.1