Re: [PATCH 0/2] fs/lock: show locks info owned by dead/invisible processes

[Konstantin Khorenko <khorenko@virtuozzo.com>]

On 08/09/2018 10:16 AM, Murphy Zhou wrote:
> Hi,
>
> Looks like this missed v4.18 ?

Hi Murphy,

yes, Jeff planned to push those patches into 4.19 and they are in "linux-next" now,
but not in 4.18 "master" currently.

On 06/14/2018 01:41 PM, Jeff Layton wrote:
 > These look fine to me. I'll plan to pick them up for v4.19 unless anyone
 > has objections.

linux-next:
1cf8e5de4055 ("fs/lock: show locks taken by processes from another pidns")
826d7bc9f013 ("fs/lock: skip lock owner pid translation in case we are in init_pid_ns")

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

> On Fri, Jun 8, 2018 at 10:27 PM, Konstantin Khorenko
> <khorenko@virtuozzo.com> wrote:
>> The behavior has been changed after 9d5b86ac13c5 ("fs/locks: Remove fl_nspid
>> and use fs-specific l_pid for remote locks")
>> and now /proc/$PID/fdinfo/$FD does not show the info about the lock
>> * if the flock owner process is dead and its pid has been already freed
>> or
>> * if the lock owner is not visible in current pidns.
>>
>> CRIU uses this interface to store locks info during dump and thus can break
>> on v4.13 and newer.
>>
>> So let's show info about locks anyway in described cases (like it was before
>> 9d5b86ac13c5), but show pid number saved in file_lock struct if we are in
>> init_pid_ns (patch 1) or just zero otherwise (patch 2) like we do with SID.
>>
>> Reproducer:
>> process A       process A1      process A2
>> fork()--------->
>> exit()          open()
>>                 flock()
>>                 fork()--------->
>>                 exit()          sleep()
>>
>> Before the patch:
>> ================
>> (root@vz7)/: cat /proc/${PID_A2}/fdinfo/3
>> pos:    4
>> flags:  02100002
>> mnt_id: 257
>> lock:   (root@vz7)/:
>>
>> After the patch:
>> ===============
>> (root@vz7)/:cat /proc/${PID_A2}/fdinfo/3
>> pos:    4
>> flags:  02100002
>> mnt_id: 295
>> lock:   1: FLOCK  ADVISORY  WRITE ${PID_A1} b6:f8a61:529946 0 EOF
>>
>> ===============
>> # cat flock1.c
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <unistd.h>
>> #include <sys/types.h>
>> #include <sys/stat.h>
>> #include <sys/file.h>
>> #include <fcntl.h>
>>
>> int main(void)
>> {
>>         int fd;
>>         int err;
>>         pid_t child_pid;
>>
>>         child_pid = fork();
>>         if (child_pid == -1)
>>                 perror("fork failed");
>>         if (child_pid) {
>>                 exit(0);
>>         }
>>
>>         fd = open("/tmp/a", O_CREAT | O_RDWR);
>>         if (fd == -1)
>>                 perror("Failed to open the file");
>>
>>         err = flock(fd, LOCK_EX);
>>         if (err == -1)
>>                 perror("flock failed");
>>
>>         child_pid = fork();
>>         if (child_pid == -1)
>>                 perror("fork failed");
>>         if (child_pid)
>>                 exit(0);
>>
>>         sleep(10000);
>>
>>         return 0;
>> }
>>
>> Konstantin Khorenko (2):
>>   fs/lock: skip lock owner pid translation in case we are in init_pid_ns
>>   fs/lock: show locks taken by processes from another pidns
>>
>>  fs/locks.c | 15 ++++++++++-----
>>  1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> --
>> 2.15.1
>>
> .
>