From: Waiman Long <longman@redhat.com>
To: Uladzislau Rezki <urezki@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/vmalloc: Fix unlock order in s_stop()
Date: Sun, 13 Dec 2020 14:42:51 -0500 [thread overview]
Message-ID: <ae1f12c5-b57f-7b40-81d5-0fdf7927c437@redhat.com> (raw)
In-Reply-To: <20201213183936.GA20007@pc636>
On 12/13/20 1:39 PM, Uladzislau Rezki wrote:
> On Sun, Dec 13, 2020 at 01:08:43PM -0500, Waiman Long wrote:
>> When multiple locks are acquired, they should be released in reverse
>> order. For s_start() and s_stop() in mm/vmalloc.c, that is not the
>> case.
>>
>> s_start: mutex_lock(&vmap_purge_lock); spin_lock(&vmap_area_lock);
>> s_stop : mutex_unlock(&vmap_purge_lock); spin_unlock(&vmap_area_lock);
>>
>> This unlock sequence, though allowed, is not optimal. If a waiter is
>> present, mutex_unlock() will need to go through the slowpath of waking
>> up the waiter with preemption disabled. Fix that by releasing the
>> spinlock first before the mutex.
>>
>> Fixes: e36176be1c39 ("mm/vmalloc: rework vmap_area_lock")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>> mm/vmalloc.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 6ae491a8b210..75913f685c71 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -3448,11 +3448,11 @@ static void *s_next(struct seq_file *m, void *p, loff_t *pos)
>> }
>>
>> static void s_stop(struct seq_file *m, void *p)
>> - __releases(&vmap_purge_lock)
>> __releases(&vmap_area_lock)
>> + __releases(&vmap_purge_lock)
>> {
>> - mutex_unlock(&vmap_purge_lock);
>> spin_unlock(&vmap_area_lock);
>> + mutex_unlock(&vmap_purge_lock);
>> }
>>
>> static void show_numa_info(struct seq_file *m, struct vm_struct *v)
> BTW, if navigation over both list is an issue, for example when there
> are multiple heavy readers of /proc/vmallocinfo, i think, it make sense
> to implement RCU safe lists iteration and get rid of both locks.
Making it lockless is certainly better, but doing lockless the right way
is tricky. I will probably keep it as it unless there is a significant
advantage of doing so.
Cheers,
Longman
>
> As for the patch: Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
>
> Thanks!
>
> --
> Vlad Rezki
>
next prev parent reply other threads:[~2020-12-13 19:44 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-13 18:08 [PATCH] mm/vmalloc: Fix unlock order in s_stop() Waiman Long
2020-12-13 18:39 ` Uladzislau Rezki
2020-12-13 19:42 ` Waiman Long [this message]
2020-12-13 21:51 ` Matthew Wilcox
2020-12-14 15:11 ` Uladzislau Rezki
2020-12-14 15:37 ` Matthew Wilcox
2020-12-14 17:56 ` Uladzislau Rezki
2020-12-14 9:39 ` David Hildenbrand
2020-12-14 15:05 ` Waiman Long
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ae1f12c5-b57f-7b40-81d5-0fdf7927c437@redhat.com \
--to=longman@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=urezki@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).