From patchwork Thu Aug 29 18:37:35 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 13783555 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97D3C1B9B21; Thu, 29 Aug 2024 18:37:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724956673; cv=none; b=S7vQYu6drYZS1jLEAYJDuGidDXV/NjD8H+vR8edfHQp+/0nM2qUcarX+ryWqzFvnUaJ0lt8/JkMoFlnObK3XdN3x4/GYNX4r4L1WzY4JoGZ3VRK2dhKtkMrTGbUENn9++UotjN1JGl5a8TJ7BxizExjNka7qdQmwqOMplG/GwiM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724956673; c=relaxed/simple; bh=5HQ56DnZm01JlMtuqxoBg8Kdzw4Qreqv0MmJ/xI2OUc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=V86qUpKSs5n9yLE5q3R2Jy+WygBd7i9lMsOlYs00rnxYzejnLUR+p4t3A2Yhxbi43QVNeuJRWkP3g6cOcvWQCQ8ZzGM0mWPdoidQW9AHYlmP/ffMfMLVAhwq+L0GhJO9oK0NmVttL6EsZvasK9PKBz1QVStTtFWRDNroU+JR3Yw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EFNfuBWg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EFNfuBWg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC7B1C4CEC1; Thu, 29 Aug 2024 18:37:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724956673; bh=5HQ56DnZm01JlMtuqxoBg8Kdzw4Qreqv0MmJ/xI2OUc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EFNfuBWgWsjVm+IBgiE5BYYh3/DMcE7xBCELmRTVGUDeKpUlExQNXzYAv4Kx2VDf3 WaefWA2jaF1yEO4Yypj/YMr7W64YoJFSj4f0C7Fnh4JX8C/Kk34G7BZ9i9NgKm9gBh oHpeYJ2roT5iLeVkdTjleNGdwRDtw6e13Sqd8B2gIn0pKOoTJB6hVLUTjT1u28BFbM Kj1Fofk6CpG+1FIGHI+Ewbr54KODXnBLo24oFvVjxXzO/R+bL9e2rdLJMfRHJ9N75U vrrKHET/k5f778b62TC8KlGKenJQnFcdE/fmwmfh0SimHCU2BgkCWX1TMCjbICf9sZ SgWCalOZfGJ0w== From: Andrii Nakryiko To: linux-trace-kernel@vger.kernel.org, peterz@infradead.org, oleg@redhat.com Cc: rostedt@goodmis.org, mhiramat@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, surenb@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, Andrii Nakryiko Subject: [PATCH v4 2/8] uprobes: protected uprobe lifetime with SRCU Date: Thu, 29 Aug 2024 11:37:35 -0700 Message-ID: <20240829183741.3331213-3-andrii@kernel.org> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20240829183741.3331213-1-andrii@kernel.org> References: <20240829183741.3331213-1-andrii@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 To avoid unnecessarily taking a (brief) refcount on uprobe during breakpoint handling in handle_swbp for entry uprobes, make find_uprobe() not take refcount, but protect the lifetime of a uprobe instance with RCU. This improves scalability, as refcount gets quite expensive due to cache line bouncing between multiple CPUs. Specifically, we utilize our own uprobe-specific SRCU instance for this RCU protection. put_uprobe() will delay actual kfree() using call_srcu(). For now, uretprobe and single-stepping handling will still acquire refcount as necessary. We'll address these issues in follow up patches by making them use SRCU with timeout. Signed-off-by: Andrii Nakryiko --- kernel/events/uprobes.c | 94 +++++++++++++++++++++++------------------ 1 file changed, 54 insertions(+), 40 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 147561c19d57..3e3595753e2c 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -41,6 +41,8 @@ static struct rb_root uprobes_tree = RB_ROOT; static DEFINE_RWLOCK(uprobes_treelock); /* serialize rbtree access */ +DEFINE_STATIC_SRCU(uprobes_srcu); + #define UPROBES_HASH_SZ 13 /* serialize uprobe->pending_list */ static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ]; @@ -59,6 +61,7 @@ struct uprobe { struct list_head pending_list; struct uprobe_consumer *consumers; struct inode *inode; /* Also hold a ref to inode */ + struct rcu_head rcu; loff_t offset; loff_t ref_ctr_offset; unsigned long flags; @@ -617,6 +620,13 @@ static inline bool uprobe_is_active(struct uprobe *uprobe) return !RB_EMPTY_NODE(&uprobe->rb_node); } +static void uprobe_free_rcu(struct rcu_head *rcu) +{ + struct uprobe *uprobe = container_of(rcu, struct uprobe, rcu); + + kfree(uprobe); +} + static void put_uprobe(struct uprobe *uprobe) { if (!refcount_dec_and_test(&uprobe->ref)) @@ -638,7 +648,7 @@ static void put_uprobe(struct uprobe *uprobe) delayed_uprobe_remove(uprobe, NULL); mutex_unlock(&delayed_uprobe_lock); - kfree(uprobe); + call_srcu(&uprobes_srcu, &uprobe->rcu, uprobe_free_rcu); } static __always_inline @@ -680,33 +690,25 @@ static inline int __uprobe_cmp(struct rb_node *a, const struct rb_node *b) return uprobe_cmp(u->inode, u->offset, __node_2_uprobe(b)); } -static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset) +/* + * Assumes being inside RCU protected region. + * No refcount is taken on returned uprobe. + */ +static struct uprobe *find_uprobe_rcu(struct inode *inode, loff_t offset) { struct __uprobe_key key = { .inode = inode, .offset = offset, }; - struct rb_node *node = rb_find(&key, &uprobes_tree, __uprobe_cmp_key); - - if (node) - return try_get_uprobe(__node_2_uprobe(node)); - - return NULL; -} + struct rb_node *node; -/* - * Find a uprobe corresponding to a given inode:offset - * Acquires uprobes_treelock - */ -static struct uprobe *find_uprobe(struct inode *inode, loff_t offset) -{ - struct uprobe *uprobe; + lockdep_assert(srcu_read_lock_held(&uprobes_srcu)); read_lock(&uprobes_treelock); - uprobe = __find_uprobe(inode, offset); + node = rb_find(&key, &uprobes_tree, __uprobe_cmp_key); read_unlock(&uprobes_treelock); - return uprobe; + return node ? __node_2_uprobe(node) : NULL; } /* @@ -1080,10 +1082,10 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new) goto free; /* * We take mmap_lock for writing to avoid the race with - * find_active_uprobe() which takes mmap_lock for reading. + * find_active_uprobe_rcu() which takes mmap_lock for reading. * Thus this install_breakpoint() can not make - * is_trap_at_addr() true right after find_uprobe() - * returns NULL in find_active_uprobe(). + * is_trap_at_addr() true right after find_uprobe_rcu() + * returns NULL in find_active_uprobe_rcu(). */ mmap_write_lock(mm); vma = find_vma(mm, info->vaddr); @@ -1885,9 +1887,13 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs) return; } + /* we need to bump refcount to store uprobe in utask */ + if (!try_get_uprobe(uprobe)) + return; + ri = kmalloc(sizeof(struct return_instance), GFP_KERNEL); if (!ri) - return; + goto fail; trampoline_vaddr = uprobe_get_trampoline_vaddr(); orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs); @@ -1914,11 +1920,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs) } orig_ret_vaddr = utask->return_instances->orig_ret_vaddr; } - /* - * uprobe's refcnt is positive, held by caller, so it's safe to - * unconditionally bump it one more time here - */ - ri->uprobe = get_uprobe(uprobe); + ri->uprobe = uprobe; ri->func = instruction_pointer(regs); ri->stack = user_stack_pointer(regs); ri->orig_ret_vaddr = orig_ret_vaddr; @@ -1929,8 +1931,9 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs) utask->return_instances = ri; return; - fail: +fail: kfree(ri); + put_uprobe(uprobe); } /* Prepare to single-step probed instruction out of line. */ @@ -1945,9 +1948,14 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr) if (!utask) return -ENOMEM; + if (!try_get_uprobe(uprobe)) + return -EINVAL; + xol_vaddr = xol_get_insn_slot(uprobe); - if (!xol_vaddr) - return -ENOMEM; + if (!xol_vaddr) { + err = -ENOMEM; + goto err_out; + } utask->xol_vaddr = xol_vaddr; utask->vaddr = bp_vaddr; @@ -1955,12 +1963,15 @@ pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr) err = arch_uprobe_pre_xol(&uprobe->arch, regs); if (unlikely(err)) { xol_free_insn_slot(current); - return err; + goto err_out; } utask->active_uprobe = uprobe; utask->state = UTASK_SSTEP; return 0; +err_out: + put_uprobe(uprobe); + return err; } /* @@ -2043,7 +2054,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) return is_trap_insn(&opcode); } -static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp) +/* assumes being inside RCU protected region */ +static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swbp) { struct mm_struct *mm = current->mm; struct uprobe *uprobe = NULL; @@ -2056,7 +2068,7 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp) struct inode *inode = file_inode(vma->vm_file); loff_t offset = vaddr_to_offset(vma, bp_vaddr); - uprobe = find_uprobe(inode, offset); + uprobe = find_uprobe_rcu(inode, offset); } if (!uprobe) @@ -2202,13 +2214,15 @@ static void handle_swbp(struct pt_regs *regs) { struct uprobe *uprobe; unsigned long bp_vaddr; - int is_swbp; + int is_swbp, srcu_idx; bp_vaddr = uprobe_get_swbp_addr(regs); if (bp_vaddr == uprobe_get_trampoline_vaddr()) return uprobe_handle_trampoline(regs); - uprobe = find_active_uprobe(bp_vaddr, &is_swbp); + srcu_idx = srcu_read_lock(&uprobes_srcu); + + uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp); if (!uprobe) { if (is_swbp > 0) { /* No matching uprobe; signal SIGTRAP. */ @@ -2224,7 +2238,7 @@ static void handle_swbp(struct pt_regs *regs) */ instruction_pointer_set(regs, bp_vaddr); } - return; + goto out; } /* change it in advance for ->handler() and restart */ @@ -2259,12 +2273,12 @@ static void handle_swbp(struct pt_regs *regs) if (arch_uprobe_skip_sstep(&uprobe->arch, regs)) goto out; - if (!pre_ssout(uprobe, regs, bp_vaddr)) - return; + if (pre_ssout(uprobe, regs, bp_vaddr)) + goto out; - /* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */ out: - put_uprobe(uprobe); + /* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */ + srcu_read_unlock(&uprobes_srcu, srcu_idx); } /*