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 --- arch/xtensa/lib/usercopy.S | 301 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 301 insertions(+) create mode 100644 arch/xtensa/lib/usercopy.S (limited to 'arch/xtensa/lib/usercopy.S') diff --git a/arch/xtensa/lib/usercopy.S b/arch/xtensa/lib/usercopy.S new file mode 100644 index 000000000..2c665c0b4 --- /dev/null +++ b/arch/xtensa/lib/usercopy.S @@ -0,0 +1,301 @@ +/* + * arch/xtensa/lib/usercopy.S + * + * Copy to/from user space (derived from arch/xtensa/lib/hal/memcopy.S) + * + * DO NOT COMBINE this function with . + * It needs to remain separate and distinct. The hal files are part + * of the Xtensa link-time HAL, and those files may differ per + * processor configuration. Patching the kernel for another + * processor configuration includes replacing the hal files, and we + * could lose the special functionality for accessing user-space + * memory during such a patch. We sacrifice a little code space here + * in favor to simplify code maintenance. + * + * This file is subject to the terms and conditions of the GNU General + * Public License. See the file "COPYING" in the main directory of + * this archive for more details. + * + * Copyright (C) 2002 Tensilica Inc. + */ + + +/* + * size_t __xtensa_copy_user (void *dst, const void *src, size_t len); + * + * The returned value is the number of bytes not copied. Implies zero + * is success. + * + * The general case algorithm is as follows: + * If the destination and source are both aligned, + * do 16B chunks with a loop, and then finish up with + * 8B, 4B, 2B, and 1B copies conditional on the length. + * If destination is aligned and source unaligned, + * do the same, but use SRC to align the source data. + * If destination is unaligned, align it by conditionally + * copying 1B and 2B and then retest. + * This code tries to use fall-through braches for the common + * case of aligned destinations (except for the branches to + * the alignment label). + * + * Register use: + * a0/ return address + * a1/ stack pointer + * a2/ return value + * a3/ src + * a4/ length + * a5/ dst + * a6/ tmp + * a7/ tmp + * a8/ tmp + * a9/ tmp + * a10/ tmp + * a11/ original length + */ + +#include +#include +#include + + .text +ENTRY(__xtensa_copy_user) + +#if !XCHAL_HAVE_LOOPS && defined(__XTENSA_CALL0_ABI__) +#define STACK_SIZE 4 +#else +#define STACK_SIZE 0 +#endif + abi_entry(STACK_SIZE) + # a2/ dst, a3/ src, a4/ len + mov a5, a2 # copy dst so that a2 is return value + mov a11, a4 # preserve original len for error case +.Lcommon: + bbsi.l a2, 0, .Ldst1mod2 # if dst is 1 mod 2 + bbsi.l a2, 1, .Ldst2mod4 # if dst is 2 mod 4 +.Ldstaligned: # return here from .Ldstunaligned when dst is aligned + srli a7, a4, 4 # number of loop iterations with 16B + # per iteration + movi a8, 3 # if source is also aligned, + bnone a3, a8, .Laligned # then use word copy + __ssa8 a3 # set shift amount from byte offset + bnez a4, .Lsrcunaligned + movi a2, 0 # return success for len==0 + abi_ret(STACK_SIZE) + +/* + * Destination is unaligned + */ + +.Ldst1mod2: # dst is only byte aligned + bltui a4, 7, .Lbytecopy # do short copies byte by byte + + # copy 1 byte +EX(10f) l8ui a6, a3, 0 + addi a3, a3, 1 +EX(10f) s8i a6, a5, 0 + addi a5, a5, 1 + addi a4, a4, -1 + bbci.l a5, 1, .Ldstaligned # if dst is now aligned, then + # return to main algorithm +.Ldst2mod4: # dst 16-bit aligned + # copy 2 bytes + bltui a4, 6, .Lbytecopy # do short copies byte by byte +EX(10f) l8ui a6, a3, 0 +EX(10f) l8ui a7, a3, 1 + addi a3, a3, 2 +EX(10f) s8i a6, a5, 0 +EX(10f) s8i a7, a5, 1 + addi a5, a5, 2 + addi a4, a4, -2 + j .Ldstaligned # dst is now aligned, return to main algorithm + +/* + * Byte by byte copy + */ + .align 4 + .byte 0 # 1 mod 4 alignment for LOOPNEZ + # (0 mod 4 alignment for LBEG) +.Lbytecopy: +#if XCHAL_HAVE_LOOPS + loopnez a4, .Lbytecopydone +#else /* !XCHAL_HAVE_LOOPS */ + beqz a4, .Lbytecopydone + add a7, a3, a4 # a7 = end address for source +#endif /* !XCHAL_HAVE_LOOPS */ +.Lnextbyte: +EX(10f) l8ui a6, a3, 0 + addi a3, a3, 1 +EX(10f) s8i a6, a5, 0 + addi a5, a5, 1 +#if !XCHAL_HAVE_LOOPS + blt a3, a7, .Lnextbyte +#endif /* !XCHAL_HAVE_LOOPS */ +.Lbytecopydone: + movi a2, 0 # return success for len bytes copied + abi_ret(STACK_SIZE) + +/* + * Destination and source are word-aligned. + */ + # copy 16 bytes per iteration for word-aligned dst and word-aligned src + .align 4 # 1 mod 4 alignment for LOOPNEZ + .byte 0 # (0 mod 4 alignment for LBEG) +.Laligned: +#if XCHAL_HAVE_LOOPS + loopnez a7, .Loop1done +#else /* !XCHAL_HAVE_LOOPS */ + beqz a7, .Loop1done + slli a8, a7, 4 + add a8, a8, a3 # a8 = end of last 16B source chunk +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop1: +EX(10f) l32i a6, a3, 0 +EX(10f) l32i a7, a3, 4 +EX(10f) s32i a6, a5, 0 +EX(10f) l32i a6, a3, 8 +EX(10f) s32i a7, a5, 4 +EX(10f) l32i a7, a3, 12 +EX(10f) s32i a6, a5, 8 + addi a3, a3, 16 +EX(10f) s32i a7, a5, 12 + addi a5, a5, 16 +#if !XCHAL_HAVE_LOOPS + blt a3, a8, .Loop1 +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop1done: + bbci.l a4, 3, .L2 + # copy 8 bytes +EX(10f) l32i a6, a3, 0 +EX(10f) l32i a7, a3, 4 + addi a3, a3, 8 +EX(10f) s32i a6, a5, 0 +EX(10f) s32i a7, a5, 4 + addi a5, a5, 8 +.L2: + bbci.l a4, 2, .L3 + # copy 4 bytes +EX(10f) l32i a6, a3, 0 + addi a3, a3, 4 +EX(10f) s32i a6, a5, 0 + addi a5, a5, 4 +.L3: + bbci.l a4, 1, .L4 + # copy 2 bytes +EX(10f) l16ui a6, a3, 0 + addi a3, a3, 2 +EX(10f) s16i a6, a5, 0 + addi a5, a5, 2 +.L4: + bbci.l a4, 0, .L5 + # copy 1 byte +EX(10f) l8ui a6, a3, 0 +EX(10f) s8i a6, a5, 0 +.L5: + movi a2, 0 # return success for len bytes copied + abi_ret(STACK_SIZE) + +/* + * Destination is aligned, Source is unaligned + */ + + .align 4 + .byte 0 # 1 mod 4 alignement for LOOPNEZ + # (0 mod 4 alignment for LBEG) +.Lsrcunaligned: + # copy 16 bytes per iteration for word-aligned dst and unaligned src + and a10, a3, a8 # save unalignment offset for below + sub a3, a3, a10 # align a3 (to avoid sim warnings only; not needed for hardware) +EX(10f) l32i a6, a3, 0 # load first word +#if XCHAL_HAVE_LOOPS + loopnez a7, .Loop2done +#else /* !XCHAL_HAVE_LOOPS */ + beqz a7, .Loop2done +#if defined(__XTENSA_CALL0_ABI__) + s32i a10, a1, 0 + slli a10, a7, 4 + add a10, a10, a3 # a10 = end of last 16B source chunk +#else + slli a12, a7, 4 + add a12, a12, a3 # a12 = end of last 16B source chunk +#endif +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop2: +EX(10f) l32i a7, a3, 4 +EX(10f) l32i a8, a3, 8 + __src_b a6, a6, a7 +EX(10f) s32i a6, a5, 0 +EX(10f) l32i a9, a3, 12 + __src_b a7, a7, a8 +EX(10f) s32i a7, a5, 4 +EX(10f) l32i a6, a3, 16 + __src_b a8, a8, a9 +EX(10f) s32i a8, a5, 8 + addi a3, a3, 16 + __src_b a9, a9, a6 +EX(10f) s32i a9, a5, 12 + addi a5, a5, 16 +#if !XCHAL_HAVE_LOOPS +#if defined(__XTENSA_CALL0_ABI__) + blt a3, a10, .Loop2 + l32i a10, a1, 0 +#else + blt a3, a12, .Loop2 +#endif +#endif /* !XCHAL_HAVE_LOOPS */ +.Loop2done: + bbci.l a4, 3, .L12 + # copy 8 bytes +EX(10f) l32i a7, a3, 4 +EX(10f) l32i a8, a3, 8 + __src_b a6, a6, a7 +EX(10f) s32i a6, a5, 0 + addi a3, a3, 8 + __src_b a7, a7, a8 +EX(10f) s32i a7, a5, 4 + addi a5, a5, 8 + mov a6, a8 +.L12: + bbci.l a4, 2, .L13 + # copy 4 bytes +EX(10f) l32i a7, a3, 4 + addi a3, a3, 4 + __src_b a6, a6, a7 +EX(10f) s32i a6, a5, 0 + addi a5, a5, 4 + mov a6, a7 +.L13: + add a3, a3, a10 # readjust a3 with correct misalignment + bbci.l a4, 1, .L14 + # copy 2 bytes +EX(10f) l8ui a6, a3, 0 +EX(10f) l8ui a7, a3, 1 + addi a3, a3, 2 +EX(10f) s8i a6, a5, 0 +EX(10f) s8i a7, a5, 1 + addi a5, a5, 2 +.L14: + bbci.l a4, 0, .L15 + # copy 1 byte +EX(10f) l8ui a6, a3, 0 +EX(10f) s8i a6, a5, 0 +.L15: + movi a2, 0 # return success for len bytes copied + abi_ret(STACK_SIZE) + +ENDPROC(__xtensa_copy_user) +EXPORT_SYMBOL(__xtensa_copy_user) + + .section .fixup, "ax" + .align 4 + +/* a2 = original dst; a5 = current dst; a11= original len + * bytes_copied = a5 - a2 + * retval = bytes_not_copied = original len - bytes_copied + * retval = a11 - (a5 - a2) + */ + + +10: + sub a2, a5, a2 /* a2 <-- bytes copied */ + sub a2, a11, a2 /* a2 <-- bytes not copied */ + abi_ret(STACK_SIZE) -- cgit v1.3.1