From: Oleksandr Natalenko <oleksandr@redhat.com>
To: Jann Horn <jannh@google.com>
Cc: kernel list <linux-kernel@vger.kernel.org>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Hugh Dickins <hughd@google.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>, Michal Hocko <mhocko@suse.com>,
Matthew Wilcox <willy@infradead.org>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Greg KH <greg@kroah.com>, Suren Baghdasaryan <surenb@google.com>,
Minchan Kim <minchan@kernel.org>,
Timofey Titovets <nefelim4ag@gmail.com>,
Aaron Tomlin <atomlin@redhat.com>,
Grzegorz Halat <ghalat@redhat.com>, Linux-MM <linux-mm@kvack.org>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH RFC 4/5] mm/ksm, proc: introduce remote merge
Date: Thu, 16 May 2019 16:43:24 +0200 [thread overview]
Message-ID: <20190516144323.pzkvs6hapf3czorz@butterfly.localdomain> (raw)
In-Reply-To: <20190516142013.sf2vitmksvbkb33f@butterfly.localdomain>
On Thu, May 16, 2019 at 04:20:13PM +0200, Oleksandr Natalenko wrote:
> > [...]
> > > @@ -2960,15 +2962,63 @@ static int proc_stack_depth(struct seq_file *m, struct pid_namespace *ns,
> > > static ssize_t madvise_write(struct file *file, const char __user *buf,
> > > size_t count, loff_t *ppos)
> > > {
> > > + /* For now, only KSM hints are implemented */
> > > +#ifdef CONFIG_KSM
> > > + char buffer[PROC_NUMBUF];
> > > + int behaviour;
> > > struct task_struct *task;
> > > + struct mm_struct *mm;
> > > + int err = 0;
> > > + struct vm_area_struct *vma;
> > > +
> > > + memset(buffer, 0, sizeof(buffer));
> > > + if (count > sizeof(buffer) - 1)
> > > + count = sizeof(buffer) - 1;
> > > + if (copy_from_user(buffer, buf, count))
> > > + return -EFAULT;
> > > +
> > > + if (!memcmp("merge", buffer, min(sizeof("merge")-1, count)))
> >
> > This means that you also match on something like "mergeblah". Just use strcmp().
>
> I agree. Just to make it more interesting I must say that
>
> /sys/kernel/mm/transparent_hugepage/enabled
>
> uses memcmp in the very same way, and thus echoing "alwaysssss" or
> "madviseeee" works perfectly there, and it was like that from the very
> beginning, it seems. Should we fix it, or it became (zomg) a public API?
Actually, maybe, the reason for using memcmp is to handle "echo"
properly: by default it puts a newline character at the end, so if we use
just strcmp, echo should be called with -n, otherwise strcmp won't match
the string.
Huh?
> [...]
--
Best regards,
Oleksandr Natalenko (post-factum)
Senior Software Maintenance Engineer
next prev parent reply other threads:[~2019-05-16 14:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-16 9:42 [PATCH RFC 0/5] mm/ksm, proc: introduce remote madvise Oleksandr Natalenko
2019-05-16 9:42 ` [PATCH RFC 1/5] proc: introduce madvise placeholder Oleksandr Natalenko
2019-05-16 9:42 ` [PATCH RFC 2/5] mm/ksm: introduce ksm_madvise_merge() helper Oleksandr Natalenko
2019-05-16 9:42 ` [PATCH RFC 3/5] mm/ksm: introduce ksm_madvise_unmerge() helper Oleksandr Natalenko
2019-05-16 9:42 ` [PATCH RFC 4/5] mm/ksm, proc: introduce remote merge Oleksandr Natalenko
2019-05-16 10:00 ` Jann Horn
2019-05-16 14:20 ` Oleksandr Natalenko
2019-05-16 14:43 ` Oleksandr Natalenko [this message]
2019-05-16 16:09 ` Jann Horn
2019-05-16 16:06 ` Jann Horn
2019-05-16 16:29 ` Aaron Tomlin
2019-05-16 9:42 ` [PATCH RFC 5/5] mm/ksm, proc: add remote madvise documentation Oleksandr Natalenko
2019-05-16 10:44 ` [PATCH RFC 0/5] mm/ksm, proc: introduce remote madvise Michal Hocko
2019-05-16 14:21 ` Oleksandr Natalenko
2019-05-16 17:24 ` Alexey Dobriyan
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