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[209.85.220.65]) by mx.google.com with SMTPS id b17sor2964006otk.53.2019.05.16.09.10.11 for (Google Transport Security); Thu, 16 May 2019 09:10:11 -0700 (PDT) Received-SPF: pass (google.com: domain of jannh@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=oQIJnd3c; spf=pass (google.com: domain of jannh@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=jannh@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=bMHMBrMd0YNkJT0fsHTTWNRBFmrV68S4uDG6Stq2kXM=; b=oQIJnd3cJFOTGWU+mhqQw5xZ/48tAUVBLW2xsdnHW75CFgSaesak+3DGKJkRVnnlf5 f7vp8/QSuZL0RRyYca0jxJkcPCNSvi7RRnbKm5rO4uvFQinoZkfWxKegO3545xUKi6Tm yDlWfRiGkBs9X7KKIzePsKsJBYU4Mhp9dgLaLpepquR4TXbJgz+SyjP4Cb13IfAyCjJc yGAprbbVJ9x317dpUPRsbFj1RHmcJ2iqPoNfYLSKY45Sx4cye8fqfTTAzGmIRMznduug 6Zyh7c9l0qYmroDn3xiUT/EZlGqq0eanNec/JAobiVm74MfwZM1Br1PUonCZzlOV+vwq 1QHw== X-Google-Smtp-Source: APXvYqxWTgXDP+q+BEeyCjiZ3kodMX94OZctQK+ZcHZRSQLNXJRMtNIbRJ4iu9fxZKt8FJF85O7xJzJohWCE0aKFlNM= X-Received: by 2002:a9d:7347:: with SMTP id l7mr6367258otk.183.1558023010974; Thu, 16 May 2019 09:10:10 -0700 (PDT) MIME-Version: 1.0 References: <20190516094234.9116-1-oleksandr@redhat.com> <20190516094234.9116-5-oleksandr@redhat.com> <20190516142013.sf2vitmksvbkb33f@butterfly.localdomain> <20190516144323.pzkvs6hapf3czorz@butterfly.localdomain> In-Reply-To: <20190516144323.pzkvs6hapf3czorz@butterfly.localdomain> From: Jann Horn Date: Thu, 16 May 2019 18:09:44 +0200 Message-ID: Subject: Re: [PATCH RFC 4/5] mm/ksm, proc: introduce remote merge To: Oleksandr Natalenko Cc: kernel list , Kirill Tkhai , Hugh Dickins , Alexey Dobriyan , Vlastimil Babka , Michal Hocko , Matthew Wilcox , Pavel Tatashin , Greg KH , Suren Baghdasaryan , Minchan Kim , Timofey Titovets , Aaron Tomlin , Grzegorz Halat , Linux-MM , Linux API Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, May 16, 2019 at 4:43 PM Oleksandr Natalenko wrote: > 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? Ah, yes, other code like e.g. proc_setgroups_write() uses strncmp() and then has an extra check to make sure everything trailing is whitespace.