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Date:   Tue, 12 Mar 2019 09:47:21 -0700
From:   Davidlohr Bueso <dbueso@suse.de>
To:     Li RongQing <lirongqing@baidu.com>
Cc:     linux-kernel@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Manfred Spraul <manfred@colorfullife.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH][v2] ipc: prevent lockup on alloc_msg and free_msg
Organization: SUSE Labs
In-Reply-To: <1552029161-4957-1-git-send-email-lirongqing@baidu.com>
References: <1552029161-4957-1-git-send-email-lirongqing@baidu.com>
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On 2019-03-07 23:12, Li RongQing wrote:
> From: Li Rongqing <lirongqing@baidu.com>
> 
> msgctl10 of ltp triggers the following lockup When CONFIG_KASAN
> is enabled on large memory SMP systems, the pages initialization
> can take a long time, if msgctl10 requests a huge block memory,
> and it will block rcu scheduler, so release cpu actively.
> 
> After adding schedule() in free_msg, free_msg can not be called
> when holding spinlock, so adding msg to a tmp list, and free it
> out of spinlock
> 
> [79441.630467] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> [79441.637566] rcu:     Tasks blocked on level-1 rcu_node (CPUs 16-31): 
> P32505
> [79441.645355] rcu:     Tasks blocked on level-1 rcu_node (CPUs 48-63): 
> P34978
> [79441.653149] rcu:     (detected by 11, t=35024 jiffies, g=44237529,
> q=16542267)
> [79441.661247] msgctl10        R  running task    21608 32505   2794 
> 0x00000082
> [79441.669455] Call Trace:
> [79441.736659]  preempt_schedule_irq+0x4c/0xb0
> [79441.741578]  retint_kernel+0x1b/0x2d
> [79441.745796] RIP: 0010:__is_insn_slot_addr+0xfb/0x250
> [79441.751595] Code: 82 1d 00 48 8b 9b 90 00 00 00 4c 89 f7 49 c1 ee
> 03 e8 59 83 1d 00 48 b8 00 00 00 00 00 fc ff df 4c 39 eb 48 89 9d 58
> ff ff ff <41> c6 04 06 f8 74 66 4c 8d 75 98 4c 89 f1 48 c1 e9 03 48 01
> c8 48
> [79441.773232] RSP: 0018:ffff88bce041f758 EFLAGS: 00000246 ORIG_RAX:
> ffffffffffffff13
> [79441.782071] RAX: dffffc0000000000 RBX: ffffffff8471bc50 RCX: 
> ffffffff828a2a57
> [79441.790337] RDX: dffffc0000000000 RSI: dffffc0000000000 RDI: 
> ffff88bce041f780
> [79441.798612] RBP: ffff88bce041f828 R08: ffffed15f3f4c5b3 R09: 
> ffffed15f3f4c5b3
> [79441.806877] R10: 0000000000000001 R11: ffffed15f3f4c5b2 R12: 
> 000000318aee9b73
> [79441.815139] R13: ffffffff8471bc50 R14: 1ffff1179c083ef0 R15: 
> 1ffff1179c083eec
> [79441.848618]  kernel_text_address+0xc1/0x100
> [79441.853542]  __kernel_text_address+0xe/0x30
> [79441.858453]  unwind_get_return_address+0x2f/0x50
> [79441.863864]  __save_stack_trace+0x92/0x100
> [79441.868742]  create_object+0x380/0x650
> [79441.911831]  __kmalloc+0x14c/0x2b0
> [79441.915874]  load_msg+0x38/0x1a0
> [79441.919726]  do_msgsnd+0x19e/0xcf0
> [79442.006475]  do_syscall_64+0x117/0x400
> [79442.037964]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> [79386.022357] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> [79386.029455] rcu:     Tasks blocked on level-1 rcu_node (CPUs 0-15): 
> P32170
> [79386.037146] rcu:     (detected by 14, t=35016 jiffies, g=44237525,
> q=12423063)
> [79386.045242] msgctl10        R  running task    21608 32170  32155 
> 0x00000082
> [79386.053447] Call Trace:
> [79386.107584]  preempt_schedule_irq+0x4c/0xb0
> [79386.112495]  retint_kernel+0x1b/0x2d
> [79386.116712] RIP: 0010:lock_acquire+0x4d/0x340
> [79386.121816] Code: 48 81 ec c0 00 00 00 45 89 c6 4d 89 cf 48 8d 6c
> 24 20 48 89 3c 24 48 8d bb e4 0c 00 00 89 74 24 0c 48 c7 44 24 20 b3
> 8a b5 41 <48> c1 ed 03 48 c7 44 24 28 b4 25 18 84 48 c7 44 24 30 d0 54
> 7a 82
> [79386.143446] RSP: 0018:ffff88af83417738 EFLAGS: 00000282 ORIG_RAX:
> ffffffffffffff13
> [79386.152278] RAX: dffffc0000000000 RBX: ffff88bd335f3080 RCX: 
> 0000000000000002
> [79386.160543] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 
> ffff88bd335f3d64
> [79386.168798] RBP: ffff88af83417758 R08: 0000000000000000 R09: 
> 0000000000000000
> [79386.177049] R10: 0000000000000001 R11: ffffed13f3f745b2 R12: 
> 0000000000000000
> [79386.185308] R13: 0000000000000002 R14: 0000000000000000 R15: 
> 0000000000000000
> [79386.213791]  is_bpf_text_address+0x32/0xe0
> [79386.223516]  kernel_text_address+0xec/0x100
> [79386.233532]  __kernel_text_address+0xe/0x30
> [79386.238448]  unwind_get_return_address+0x2f/0x50
> [79386.243858]  __save_stack_trace+0x92/0x100
> [79386.252648]  save_stack+0x32/0xb0
> [79386.357923]  __kasan_slab_free+0x130/0x180
> [79386.362745]  kfree+0xfa/0x2d0
> [79386.366291]  free_msg+0x24/0x50
> [79386.370020]  do_msgrcv+0x508/0xe60
> [79386.446596]  do_syscall_64+0x117/0x400
> [79386.478122]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>
> Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> ---
> v1 -->v2: move free_msg out of spinlock in mqueue_evict_inode
>           move schedule() from loop end to loop start, since it does
> not isolate two kmallocs in loop end
> 
> 
>  ipc/mqueue.c  | 10 ++++++++--
>  ipc/msgutil.c |  6 ++++++
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/ipc/mqueue.c b/ipc/mqueue.c
> index c0d58f390..bce7af154 100644
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -391,7 +391,8 @@ static void mqueue_evict_inode(struct inode *inode)
>  	struct user_struct *user;
>  	unsigned long mq_bytes, mq_treesize;
>  	struct ipc_namespace *ipc_ns;
> -	struct msg_msg *msg;
> +	struct msg_msg *msg, *nmsg;
> +	LIST_HEAD(tmp_msg);
> 
>  	clear_inode(inode);
> 
> @@ -402,10 +403,15 @@ static void mqueue_evict_inode(struct inode 
> *inode)
>  	info = MQUEUE_I(inode);
>  	spin_lock(&info->lock);
>  	while ((msg = msg_get(info)) != NULL)
> -		free_msg(msg);
> +		list_add_tail(&msg->m_list, &tmp_msg);
>  	kfree(info->node_cache);
>  	spin_unlock(&info->lock);

So after releasing the lock, the msg rbtree/list is empty and new calls 
will not see those in the newly populated tmp_msg list, and therefore 
they cannot access the delayed msg freeing pointers, which is good. Also 
the fact that the node_cache is now freed before the actual messages 
seems to be harmless as this is wanted for msg_insert() avoiding 
GFP_ATOMIC allocations, and after releasing the info->lock the thing is 
freed anyway so it should not change things.

Feel free to add my:

Reviewed-by: Davidlohr Bueso <dbueso@suse.de>

> 
> +	list_for_each_entry_safe(msg, nmsg, &tmp_msg, m_list) {
> +		list_del(&msg->m_list);
> +		free_msg(msg);
> +	}
> +
>  	/* Total amount of bytes accounted for the mqueue */
>  	mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
>  		min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
> diff --git a/ipc/msgutil.c b/ipc/msgutil.c
> index 84598025a..e65593742 100644
> --- a/ipc/msgutil.c
> +++ b/ipc/msgutil.c
> @@ -18,6 +18,7 @@
>  #include <linux/utsname.h>
>  #include <linux/proc_ns.h>
>  #include <linux/uaccess.h>
> +#include <linux/sched.h>
> 
>  #include "util.h"
> 
> @@ -64,6 +65,9 @@ static struct msg_msg *alloc_msg(size_t len)
>  	pseg = &msg->next;
>  	while (len > 0) {
>  		struct msg_msgseg *seg;
> +
> +		cond_resched();
> +
>  		alen = min(len, DATALEN_SEG);
>  		seg = kmalloc(sizeof(*seg) + alen, GFP_KERNEL_ACCOUNT);
>  		if (seg == NULL)
> @@ -176,6 +180,8 @@ void free_msg(struct msg_msg *msg)
>  	kfree(msg);
>  	while (seg != NULL) {
>  		struct msg_msgseg *tmp = seg->next;
> +
> +		cond_resched();
>  		kfree(seg);
>  		seg = tmp;
>  	}