A CPU's current task can have its {closid, rmid} fields read locally while
they are being concurrently written to from another CPU. This can happen
anytime __resctrl_sched_in() races with e.g. a __rdtgroup_move_task() call
on a different CPU targeting the first CPU's current task.Prevent load / store tearing for those accesses by giving them the READ_ONCE() / WRITE_ONCE() treatment. Reviewed-by: James Morse <[email protected]> Signed-off-by: Valentin Schneider <[email protected]> --- arch/x86/include/asm/resctrl.h | 11 +++++++---- arch/x86/kernel/cpu/resctrl/rdtgroup.c | 24 +++++++++++++----------- 2 files changed, 20 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h index 07603064df8f..d60ed0668a59 100644 --- a/arch/x86/include/asm/resctrl.h +++ b/arch/x86/include/asm/resctrl.h @@ -56,19 +56,22 @@ static void __resctrl_sched_in(void) struct resctrl_pqr_state *state = this_cpu_ptr(&pqr_state); u32 closid = state->default_closid; u32 rmid = state->default_rmid; + u32 tmp; /* * If this task has a closid/rmid assigned, use it. * Else use the closid/rmid assigned to this cpu. */ if (static_branch_likely(&rdt_alloc_enable_key)) { - if (current->closid) - closid = current->closid; + tmp = READ_ONCE(current->closid); + if (tmp) + closid = tmp; } if (static_branch_likely(&rdt_mon_enable_key)) { - if (current->rmid) - rmid = current->rmid; + tmp = READ_ONCE(current->rmid); + if (tmp) + rmid = tmp; } if (closid != state->cur_closid || rmid != state->cur_rmid) { diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c index f62d81104fd0..135a51529f70 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -529,8 +529,8 @@ static void move_myself(struct callback_head *head) */ if (atomic_dec_and_test(&rdtgrp->waitcount) && (rdtgrp->flags & RDT_DELETED)) { - current->closid = 0; - current->rmid = 0; + WRITE_ONCE(current->closid, 0); + WRITE_ONCE(current->rmid, 0); kfree(rdtgrp); } @@ -565,8 +565,8 @@ static int __rdtgroup_move_task(struct task_struct *tsk, * their parent CTRL group. */ if (rdtgrp->type == RDTCTRL_GROUP) - tsk->closid = rdtgrp->closid; - tsk->rmid = rdtgrp->mon.rmid; + WRITE_ONCE(tsk->closid, rdtgrp->closid); + WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid); /* * Take a refcount, so rdtgrp cannot be freed before the @@ -598,13 +598,15 @@ static int __rdtgroup_move_task(struct task_struct *tsk, static bool is_closid_match(struct task_struct *t, struct rdtgroup *r) { return (rdt_alloc_capable && - (r->type == RDTCTRL_GROUP) && (t->closid == r->closid)); + (r->type == RDTCTRL_GROUP) && + (READ_ONCE(t->closid) == r->closid)); } static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r) { return (rdt_mon_capable && - (r->type == RDTMON_GROUP) && (t->rmid == r->mon.rmid)); + (r->type == RDTMON_GROUP) && + (READ_ONCE(t->rmid) == r->mon.rmid)); } /** @@ -680,7 +682,7 @@ static int rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp, goto out; if (rdtgrp->type == RDTMON_GROUP && - rdtgrp->mon.parent->closid != tsk->closid) { + rdtgrp->mon.parent->closid != READ_ONCE(tsk->closid)) { rdt_last_cmd_puts("Can't move task to different control group\n"); ret = -EINVAL; goto out; @@ -810,7 +812,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns, rdtg->mode != RDT_MODE_EXCLUSIVE) continue; - if (rdtg->closid != tsk->closid) + if (rdtg->closid != READ_ONCE(tsk->closid)) continue; seq_printf(s, "res:%s%s\n", (rdtg == &rdtgroup_default) ? "/" : "", @@ -818,7 +820,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns, seq_puts(s, "mon:"); list_for_each_entry(crg, &rdtg->mon.crdtgrp_list, mon.crdtgrp_list) { - if (tsk->rmid != crg->mon.rmid) + if (READ_ONCE(tsk->rmid) != crg->mon.rmid) continue; seq_printf(s, "%s", crg->kn->name); break; @@ -2336,8 +2338,8 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to, for_each_process_thread(p, t) { if (!from || is_closid_match(t, from) || is_rmid_match(t, from)) { - t->closid = to->closid; - t->rmid = to->mon.rmid; + WRITE_ONCE(t->closid, to->closid); + WRITE_ONCE(t->rmid, to->mon.rmid); #ifdef CONFIG_SMP /* -- 2.27.0
