From: Michal Hocko <mhocko@kernel.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: gorcunov@gmail.com, akpm@linux-foundation.org,
arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be,
ldufour@linux.ibm.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, mguzik@redhat.com, rppt@linux.ibm.com,
vbabka@suse.cz, ktkhai@virtuozzo.com
Subject: Re: [PATCH v3 2/2] prctl_set_mm: downgrade mmap_sem to read lock
Date: Tue, 7 May 2019 19:42:15 +0200 [thread overview]
Message-ID: <20190507174215.GT31017@dhcp22.suse.cz> (raw)
In-Reply-To: <20190502125203.24014-3-mkoutny@suse.com>
On Thu 02-05-19 14:52:03, Michal Koutny wrote:
> The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap
> semaphore taken.") added synchronization of reading argument/environment
> boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce
> arg_lock to protect arg_start|end and env_start|end in mm_struct")
> avoided the coarse use of mmap_sem in similar situations. But there
> still remained two places that (mis)use mmap_sem.
>
> get_cmdline should also use arg_lock instead of mmap_sem when it reads the
> boundaries.
>
> The second place that should use arg_lock is in prctl_set_mm. By
> protecting the boundaries fields with the arg_lock, we can downgrade
> mmap_sem to reader lock (analogous to what we already do in
> prctl_set_mm_map).
>
> v2: call find_vma without arg_lock held
> v3: squashed get_cmdline arg_lock patch
>
> Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
> Cc: Yang Shi <yang.shi@linux.alibaba.com>
> Cc: Mateusz Guzik <mguzik@redhat.com>
> CC: Cyrill Gorcunov <gorcunov@gmail.com>
> Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> Signed-off-by: Michal Koutný <mkoutny@suse.com>
Just a nit. S-o-b chain is not correct here. The first s-o-b should
match the author (From) of the patch.
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> kernel/sys.c | 10 ++++++++--
> mm/util.c | 4 ++--
> 2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 5e0a5edf47f8..14be57840511 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2122,9 +2122,14 @@ static int prctl_set_mm(int opt, unsigned long addr,
>
> error = -EINVAL;
>
> - down_write(&mm->mmap_sem);
> + /*
> + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for
> + * a) concurrent sys_brk, b) finding VMA for addr validation.
> + */
> + down_read(&mm->mmap_sem);
> vma = find_vma(mm, addr);
>
> + spin_lock(&mm->arg_lock);
> prctl_map.start_code = mm->start_code;
> prctl_map.end_code = mm->end_code;
> prctl_map.start_data = mm->start_data;
> @@ -2212,7 +2217,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
>
> error = 0;
> out:
> - up_write(&mm->mmap_sem);
> + spin_unlock(&mm->arg_lock);
> + up_read(&mm->mmap_sem);
> return error;
> }
>
> diff --git a/mm/util.c b/mm/util.c
> index 43a2984bccaa..5cf0e84a0823 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
> if (!mm->arg_end)
> goto out_mm; /* Shh! No looking before we're done */
>
> - down_read(&mm->mmap_sem);
> + spin_lock(&mm->arg_lock);
> arg_start = mm->arg_start;
> arg_end = mm->arg_end;
> env_start = mm->env_start;
> env_end = mm->env_end;
> - up_read(&mm->mmap_sem);
> + spin_unlock(&mm->arg_lock);
>
> len = arg_end - arg_start;
>
> --
> 2.16.4
--
Michal Hocko
SUSE Labs
prev parent reply other threads:[~2019-05-07 17:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-17 12:03 [PATCH] mm: get_cmdline use arg_lock instead of mmap_sem Michal Koutný
2019-04-17 13:41 ` Michal Hocko
2019-04-17 14:41 ` Michal Koutný
2019-04-17 14:55 ` Michal Hocko
2019-04-18 13:50 ` [PATCH] prctl_set_mm: downgrade mmap_sem to read lock Michal Koutný
2019-04-18 14:09 ` Cyrill Gorcunov
2019-04-18 14:15 ` Michal Hocko
2019-04-18 14:27 ` Laurent Dufour
2019-04-18 18:23 ` Cyrill Gorcunov
2019-04-30 8:18 ` [PATCH 0/3] Reduce mmap_sem usage for args manipulation Michal Koutný
2019-04-30 8:18 ` [PATCH 1/3] mm: get_cmdline use arg_lock instead of mmap_sem Michal Koutný
2019-04-30 9:09 ` Kirill Tkhai
2019-04-30 9:38 ` Cyrill Gorcunov
2019-04-30 9:53 ` Kirill Tkhai
2019-04-30 10:45 ` Cyrill Gorcunov
2019-04-30 10:56 ` Michal Koutný
2019-04-30 13:24 ` Cyrill Gorcunov
2019-04-30 8:18 ` [PATCH 2/3] prctl_set_mm: Refactor checks from validate_prctl_map Michal Koutný
2019-04-30 9:27 ` Kirill Tkhai
2019-04-30 8:18 ` [PATCH 3/3] prctl_set_mm: downgrade mmap_sem to read lock Michal Koutný
2019-04-30 8:55 ` Kirill Tkhai
2019-04-30 9:08 ` Cyrill Gorcunov
2019-04-30 9:11 ` Kirill Tkhai
2019-05-02 12:52 ` [PATCH v3 0/2] Reduce mmap_sem usage for args manipulation Michal Koutný
2019-05-02 12:52 ` [PATCH v3 1/2] prctl_set_mm: Refactor checks from validate_prctl_map Michal Koutný
2019-05-02 20:57 ` Cyrill Gorcunov
2019-05-02 12:52 ` [PATCH v3 2/2] prctl_set_mm: downgrade mmap_sem to read lock Michal Koutný
2019-05-02 20:57 ` Cyrill Gorcunov
2019-05-06 9:28 ` Kirill Tkhai
2019-05-07 17:42 ` Michal Hocko [this message]
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