Hi Jan,
The limitation is added by the following patch. In some old kernel
versions, no limitation is applied. I suggest that tst_kvercmp should be
used in this case.
commit f2302505775fd13ba93f034206f1e2a587017929
Author: Andrew Vagin <ava...@openvz.org>
Date: Thu Oct 25 13:38:07 2012 -0700
pidns: limit the nesting depth of pid namespaces
'struct pid' is a "variable sized struct" - a header with an array of
upids at the end.
The size of the array depends on a level (depth) of pid
namespaces. Now a
level of pidns is not limited, so 'struct pid' can be more than one
page.
Looks reasonable, that it should be less than a page.
MAX_PIS_NS_LEVEL is
not calculated from PAGE_SIZE, because in this case it depends on
architectures, config options and it will be reduced, if someone adds a
new fields in struct pid or struct upid.
I suggest to set MAX_PIS_NS_LEVEL = 32, because it saves ability to
expand
"struct pid" and it's more than enough for all known for me use-cases.
When someone finds a reasonable use case, we can add a config
option or a
sysctl parameter.
In addition it will reduce the effect of another problem, when we have
many nested namespaces and the oldest one starts dying.
zap_pid_ns_processe will be called for each namespace and find_vpid
will
be called for each process in a namespace. find_vpid will be called
minimum max_level^2 / 2 times. The reason of that is that when we
found a
bit in pidmap, we can't determine this pidns is top for this
process or it
isn't.
vpid is a heavy operation, so a fork bomb, which create many nested
namespace, can make a system inaccessible for a long time. For
example my
system becomes inaccessible for a few minutes with 4000 processes.
Regards,
Yuan
On 2015/8/5 20:25, Jan Stancek wrote:
>
>
>
> ----- Original Message -----
>> From: "Yuan Sun" <sunyu...@huawei.com>
>> To: jstan...@redhat.com
>> Cc: ltp-list@lists.sourceforge.net
>> Sent: Wednesday, 22 July, 2015 3:00:25 PM
>> Subject: [PATCH] container: new testcase pidns32
>>
> Hi,
>
>> Kernel imposes a limit of 32 nested levels of pid namespaces.
> I have some concerns about this number. It looks more like
> implementation detail. Also it doesn't seem to apply for all
> kernels out there.
>
>> Signed-off-by: Yuan Sun <sunyu...@huawei.com>
>> ---
>> testcases/kernel/containers/pidns/.gitignore | 1 +
>> testcases/kernel/containers/pidns/pidns32.c | 113
> You're missing runtest entry.
>
>> +++++++++++++++++++++++++++
>> 2 files changed, 114 insertions(+)
>> create mode 100644 testcases/kernel/containers/pidns/pidns32.c
>>
>> diff --git a/testcases/kernel/containers/pidns/.gitignore
>> b/testcases/kernel/containers/pidns/.gitignore
>> index e56c1f9..488b045 100644
>> --- a/testcases/kernel/containers/pidns/.gitignore
>> +++ b/testcases/kernel/containers/pidns/.gitignore
>> @@ -12,3 +12,4 @@
>> /pidns20
>> /pidns30
>> /pidns31
>> +/pidns32
>> diff --git a/testcases/kernel/containers/pidns/pidns32.c
>> b/testcases/kernel/containers/pidns/pidns32.c
>> new file mode 100644
>> index 0000000..8a4459b
>> --- /dev/null
>> +++ b/testcases/kernel/containers/pidns/pidns32.c
>> @@ -0,0 +1,113 @@
>> +/*
>> + * Copyright (c) Huawei Technologies Co., Ltd., 2015
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
>> + * the GNU General Public License for more details.
>> + */
>> +
>> +/*
>> + * Verify that:
>> + * The kernel imposes a limit of 32 nested levels of pid namespaces.
>> + */
>> +
>> +#define _GNU_SOURCE
>> +#include <sys/wait.h>
>> +#include <assert.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <unistd.h>
>> +#include <string.h>
>> +#include <errno.h>
>> +#include "test.h"
>> +#include "pidns_helper.h"
>> +
>> +#define MAXNEST 32
>> +
>> +char *TCID = "pidns32";
>> +int TST_TOTAL = 1;
>> +
>> +static void setup(void)
>> +{
> This should probably include tst_require_root too, since CLONE_NEWPID
> requires CAP_SYS_ADMIN.
>
>> + check_newpid();
>> + tst_tmpdir();
>> +}
>> +
>> +static void cleanup(void)
>> +{
>> + tst_rmdir();
>> +}
>> +
>> +static int child_fn1(void *arg)
>> +{
>> + pid_t cpid1;
>> + long level = (long)arg;
>> +
>> + cpid1 = ltp_clone_quick(CLONE_NEWPID | SIGCHLD,
>> + (void *)child_fn1, (void *)(level + 1));
> You are relying on clone failing and you check level only after that.
> If I take sufficiently old kernel (which doesn't impose 32 levels as maximum),
> the testcase runs until it's killed by OOM.
>
>> + if (cpid1 < 0) {
>> + if (level == (MAXNEST))
>> + return 0;
>> + return 1;
>> + }
>> + if (waitpid(cpid1, NULL, 0) == -1)
>> + return 1;
>> + return 0;
>> +}
>> +
>> +static int wait4child(pid_t pid, const char *msg)
>> +{
>> + int status;
>> +
>> + if (waitpid(pid, &status, 0) == -1) {
>> + tst_brkm(TBROK | TERRNO, cleanup, "waitpid");
>> + } else if (WIFSIGNALED(status)) {
>> + tst_resm(TFAIL, "%s: child was killed with signal = %d",
>> + msg, WTERMSIG(status));
>> + return WTERMSIG(status);
>> + } else if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
>> + tst_resm(TFAIL, "%s: child returns %d", msg, status);
>> + return WEXITSTATUS(status);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void test_max_nest(void)
>> +{
>> + pid_t cpid1;
>> + int status;
>> +
>> + cpid1 = ltp_clone_quick(CLONE_NEWPID | SIGCHLD,
>> + (void *)child_fn1, (void *)1);
>> + if (cpid1 < 0)
>> + tst_brkm(TBROK | TERRNO, cleanup, "clone failed");
>> +
>> + status = 0;
>> + status |= wait4child(cpid1, "child1");
>> + if (status == 0)
>> + tst_resm(TPASS, "The function works well.");
>> + else
>> + tst_resm(TFAIL, "Some child reported failure.");
> This can be replaced by using tst_record_childstatus().
>
> Regards,
> Jan
>
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> + int lc;
>> +
>> + setup();
>> + tst_parse_opts(argc, argv, NULL, NULL);
>> +
>> + for (lc = 0; TEST_LOOPING(lc); lc++) {
>> + tst_count = 0;
>> + test_max_nest();
>> + }
>> +
>> + cleanup();
>> + tst_exit();
>> +}
>> --
>> 1.9.1
>>
>>
> .
>
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