From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226UZewrxcJDkDDMzyS0AAM7t5VosrH0rQyRB2uNzEDo9P3gRzcTJihnDJ93q4c47CUhjSbs ARC-Seal: i=1; a=rsa-sha256; t=1517256609; cv=none; d=google.com; s=arc-20160816; b=kcMJmRprqYHrp4XUHXXH5qVbHZFbQontSurhL2w9RvRXUSTAzAuKHInJfDhBqSSNSG BW+fAFr/S9DxPVnTDMKeNXaAtiNUdbpt8cPqWrtgreZUYCP4GhATZ/lGgT2pWI/rlBVp pmtJ26C2dxxZXZ2GYl15Wa4yVFsvpsP9eWtJulfI0qN94OqJuUT66lMUg6/7P8lixYpG 8nNQ65jnqxaK0aFkNeBM5av6ytlgSG1qwn383c/BOUvN2+CozDq4T9/NIE6heMHsx1iU umpq6y+STNpq1Le5SPWf/4yBU5ec7RgUuKjeN+g91LEBXPntlVQpP1eaAsUq0tCX547U H6IQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=boHSCSrR6DybegwJpLpO0bACPNpQ6pxc7EiQhrFW3W4=; b=KiwhCYY/6vR76aaOps+7J+N5UmwKDADOOWHv8f6860xqfs7GjbkokLioW/MXgkH1e5 WlXqU197TQvonDabgugPk1zzOQ3uJtC3dml0cB5QzZMAteqFQdQLQyB31ng3q7Hlzxxl bDMFnU7iatqk9u5sOh2Xshuvxs25omVLuEUF+D2b96Jjk6+kzhLyviWoDDRAeOAZt9J9 c6sWI0/dyeoLJmdUOo5qEmh37s15PT0UJlhP2yWeJuvAps1jCoOt34rjTXeHmBay8jL6 iWSxnCFqaz1KwwsWkasoZSrBfYhoTvQKRCM9zXyyKaSzpukQ7k8oVYjCrl9ITRKt3yj6 TEuA== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.71.90 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vlastimil Babka , Michal Hocko , Alexander Viro , Eric Dumazet , David Laight , Hillf Danton , Nicholas Piggin , Jason Baron , Andrew Morton , Linus Torvalds Subject: [PATCH 4.4 20/74] fs/select: add vmalloc fallback for select(2) Date: Mon, 29 Jan 2018 13:56:25 +0100 Message-Id: <20180129123848.523118725@linuxfoundation.org> X-Mailer: git-send-email 2.16.1 In-Reply-To: <20180129123847.507563674@linuxfoundation.org> References: <20180129123847.507563674@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1590958866529927320?= X-GMAIL-MSGID: =?utf-8?q?1590958866529927320?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vlastimil Babka commit 2d19309cf86883f634a4f8ec55a54bda87db19bf upstream. The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows with the number of fds passed. We had a customer report page allocation failures of order-4 for this allocation. This is a costly order, so it might easily fail, as the VM expects such allocation to have a lower-order fallback. Such trivial fallback is vmalloc(), as the memory doesn't have to be physically contiguous and the allocation is temporary for the duration of the syscall only. There were some concerns, whether this would have negative impact on the system by exposing vmalloc() to userspace. Although an excessive use of vmalloc can cause some system wide performance issues - TLB flushes etc. - a large order allocation is not for free either and an excessive reclaim/compaction can have a similar effect. Also note that the size is effectively limited by RLIMIT_NOFILE which defaults to 1024 on the systems I checked. That means the bitmaps will fit well within single page and thus the vmalloc() fallback could be only excercised for processes where root allows a higher limit. Note that the poll(2) syscall seems to use a linked list of order-0 pages, so it doesn't need this kind of fallback. [eric.dumazet@gmail.com: fix failure path logic] [akpm@linux-foundation.org: use proper type for size] Link: http://lkml.kernel.org/r/20160927084536.5923-1-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Cc: Alexander Viro Cc: Eric Dumazet Cc: David Laight Cc: Hillf Danton Cc: Nicholas Piggin Cc: Jason Baron Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/select.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) --- a/fs/select.c +++ b/fs/select.c @@ -29,6 +29,7 @@ #include #include #include +#include #include @@ -550,7 +551,7 @@ int core_sys_select(int n, fd_set __user fd_set_bits fds; void *bits; int ret, max_fds; - unsigned int size; + size_t size, alloc_size; struct fdtable *fdt; /* Allocate small arguments on the stack to save memory and be faster */ long stack_fds[SELECT_STACK_ALLOC/sizeof(long)]; @@ -577,7 +578,14 @@ int core_sys_select(int n, fd_set __user if (size > sizeof(stack_fds) / 6) { /* Not enough space in on-stack array; must use kmalloc */ ret = -ENOMEM; - bits = kmalloc(6 * size, GFP_KERNEL); + if (size > (SIZE_MAX / 6)) + goto out_nofds; + + alloc_size = 6 * size; + bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN); + if (!bits && alloc_size > PAGE_SIZE) + bits = vmalloc(alloc_size); + if (!bits) goto out_nofds; } @@ -614,7 +622,7 @@ int core_sys_select(int n, fd_set __user out: if (bits != stack_fds) - kfree(bits); + kvfree(bits); out_nofds: return ret; }