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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrei Vagin <avagin@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
        Yuyang Du <duyuyang@gmail.com>,
        David Hildenbrand <david@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        David Howells <dhowells@redhat.com>,
        James Morris <jamorris@linux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Shakeel Butt <shakeelb@google.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Christian Kellner <christian@kellner.me>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
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        "linux-mm\@kvack.org" <linux-mm@kvack.org>,
        "stable\@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-api\@vger.kernel.org" <linux-api@vger.kernel.org>
References: <AM6PR03MB5170EB4427BF5C67EE98FF09E4E60@AM6PR03MB5170.eurprd03.prod.outlook.com>
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        <AM6PR03MB517053AED7DC89F7C0704B7DE4E50@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <AM6PR03MB51703B44170EAB4626C9B2CAE4E20@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87tv32cxmf.fsf_-_@x220.int.ebiederm.org>
        <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org>
        <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org>
        <AM6PR03MB5170BC58D90BAD80CDEF3F8BE4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <878sk94eay.fsf@x220.int.ebiederm.org>
        <AM6PR03MB517086003BD2C32E199690A3E4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87r1y12yc7.fsf@x220.int.ebiederm.org>
        <87k13t2xpd.fsf@x220.int.ebiederm.org>
        <87d09l2x5n.fsf@x220.int.ebiederm.org>
        <AM6PR03MB5170F0F9DC18F5EA77C9A857E4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <871rq12vxu.fsf@x220.int.ebiederm.org>
        <AM6PR03MB5170DF45E3245F55B95CCD91E4FE0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <877dzt1fnf.fsf@x220.int.ebiederm.org>
        <AM6PR03MB517033EAD25BED15CC84E17DE4FF0@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date:   Tue, 10 Mar 2020 10:13:42 -0500
In-Reply-To: <AM6PR03MB517033EAD25BED15CC84E17DE4FF0@AM6PR03MB5170.eurprd03.prod.outlook.com>
        (Bernd Edlinger's message of "Tue, 10 Mar 2020 14:43:41 +0100")
Message-ID: <87d09kxmxl.fsf@x220.int.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH 1/4] exec: Fix a deadlock in ptrace
Sender: linux-kernel-owner@vger.kernel.org
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Bernd Edlinger <bernd.edlinger@hotmail.de> writes:

> This fixes a deadlock in the tracer when tracing a multi-threaded
> application that calls execve while more than one thread are running.
>
> I observed that when running strace on the gcc test suite, it always
> blocks after a while, when expect calls execve, because other threads
> have to be terminated.  They send ptrace events, but the strace is no
> longer able to respond, since it is blocked in vm_access.
>
> The deadlock is always happening when strace needs to access the
> tracees process mmap, while another thread in the tracee starts to
> execve a child process, but that cannot continue until the
> PTRACE_EVENT_EXIT is handled and the WIFEXITED event is received:

Overall this looks good.  Mind if I change the subject to:
"exec: Fix a deadlock in strace" ?

Eric


>
> strace          D    0 30614  30584 0x00000000
> Call Trace:
> __schedule+0x3ce/0x6e0
> schedule+0x5c/0xd0
> schedule_preempt_disabled+0x15/0x20
> __mutex_lock.isra.13+0x1ec/0x520
> __mutex_lock_killable_slowpath+0x13/0x20
> mutex_lock_killable+0x28/0x30
> mm_access+0x27/0xa0
> process_vm_rw_core.isra.3+0xff/0x550
> process_vm_rw+0xdd/0xf0
> __x64_sys_process_vm_readv+0x31/0x40
> do_syscall_64+0x64/0x220
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> expect          D    0 31933  30876 0x80004003
> Call Trace:
> __schedule+0x3ce/0x6e0
> schedule+0x5c/0xd0
> flush_old_exec+0xc4/0x770
> load_elf_binary+0x35a/0x16c0
> search_binary_handler+0x97/0x1d0
> __do_execve_file.isra.40+0x5d4/0x8a0
> __x64_sys_execve+0x49/0x60
> do_syscall_64+0x64/0x220
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> This changes mm_access to use the new exec_update_mutex
> instead of cred_guard_mutex.
>
> This patch is based on the following patch by Eric W. Biederman:
> "[PATCH 0/5] Infrastructure to allow fixing exec deadlocks"
> Link: https://lore.kernel.org/lkml/87v9ne5y4y.fsf_-_@x220.int.ebiederm.org/
>
> Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
> ---
>  kernel/fork.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index c12595a..5720ff3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1224,7 +1224,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
>  	struct mm_struct *mm;
>  	int err;
>  
> -	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
> +	err =  mutex_lock_killable(&task->signal->exec_update_mutex);
>  	if (err)
>  		return ERR_PTR(err);
>  
> @@ -1234,7 +1234,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
>  		mmput(mm);
>  		mm = ERR_PTR(-EACCES);
>  	}
> -	mutex_unlock(&task->signal->cred_guard_mutex);
> +	mutex_unlock(&task->signal->exec_update_mutex);
>  
>  	return mm;
>  }