linux-stable.git/kernel/fork.c, branch v3.4.112

introduce for_each_thread() to replace the buggy while_each_thread()

2015-02-02T09:04:55+00:00

commit 0c740d0afc3bff0a097ad03a1c8df92757516f5c upstream.

while_each_thread() and next_thread() should die, almost every lockless
usage is wrong.

1. Unless g == current, the lockless while_each_thread() is not safe.

   while_each_thread(g, t) can loop forever if g exits, next_thread()
   can't reach the unhashed thread in this case. Note that this can
   happen even if g is the group leader, it can exec.

2. Even if while_each_thread() itself was correct, people often use
   it wrongly.

   It was never safe to just take rcu_read_lock() and loop unless
   you verify that pid_alive(g) == T, even the first next_thread()
   can point to the already freed/reused memory.

This patch adds signal_struct->thread_head and task->thread_node to
create the normal rcu-safe list with the stable head.  The new
for_each_thread(g, t) helper is always safe under rcu_read_lock() as
long as this task_struct can't go away.

Note: of course it is ugly to have both task_struct->thread_node and the
old task_struct->thread_group, we will kill it later, after we change
the users of while_each_thread() to use for_each_thread().

Perhaps we can kill it even before we convert all users, we can
reimplement next_thread(t) using the new thread_head/thread_node.  But
we can't do this right now because this will lead to subtle behavioural
changes.  For example, do/while_each_thread() always sees at least one
task, while for_each_thread() can do nothing if the whole thread group
has died.  Or thread_group_empty(), currently its semantics is not clear
unless thread_group_leader(p) and we need to audit the callers before we
can change it.

So this patch adds the new interface which has to coexist with the old
one for some time, hopefully the next changes will be more or less
straightforward and the old one will go away soon.

Signed-off-by: Oleg Nesterov 
Reviewed-by: Sergey Dyasly 
Tested-by: Sergey Dyasly 
Reviewed-by: Sameer Nanda 
Acked-by: David Rientjes 
Cc: "Eric W. Biederman" 
Cc: Frederic Weisbecker 
Cc: Mandeep Singh Baines 
Cc: "Ma, Xindong" 
Cc: Michal Hocko 
Cc: "Tu, Xiaobing" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Zefan Li

kernel/fork.c:copy_process(): unify CLONE_THREAD-or-thread_group_leader code

2015-02-02T09:04:55+00:00

commit 80628ca06c5d42929de6bc22c0a41589a834d151 upstream.

Cleanup and preparation for the next changes.

Move the "if (clone_flags & CLONE_THREAD)" code down under "if
(likely(p->pid))" and turn it into into the "else" branch.  This makes the
process/thread initialization more symmetrical and removes one check.

Signed-off-by: Oleg Nesterov 
Cc: "Eric W. Biederman" 
Cc: Michal Hocko 
Cc: Pavel Emelyanov 
Cc: Sergey Dyasly 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Zefan Li

perf: fix perf bug in fork()

2014-12-01T10:02:40+00:00

commit 6c72e3501d0d62fc064d3680e5234f3463ec5a86 upstream.

Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by
calling perf_event_free_task() when failing sched_fork() we will not yet
have done the memset() on ->perf_event_ctxp[] and will therefore try and
'free' the inherited contexts, which are still in use by the parent
process.  This is bad..

Suggested-by: Oleg Nesterov 
Reported-by: Oleg Nesterov 
Reported-by: Sylvain 'ythier' Hitier 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Zefan Li

tracing: Fix syscall_*regfunc() vs copy_process() race

2014-07-07T01:49:20+00:00

commit 4af4206be2bd1933cae20c2b6fb2058dbc887f7c upstream.

syscall_regfunc() and syscall_unregfunc() should set/clear
TIF_SYSCALL_TRACEPOINT system-wide, but do_each_thread() can race
with copy_process() and miss the new child which was not added to
the process/thread lists yet.

Change copy_process() to update the child's TIF_SYSCALL_TRACEPOINT
under tasklist.

Link: http://lkml.kernel.org/p/20140413185854.GB20668@redhat.com

Fixes: a871bd33a6c0 "tracing: Add syscall tracepoints"
Acked-by: Frederic Weisbecker 
Acked-by: Paul E. McKenney 
Signed-off-by: Oleg Nesterov 
Signed-off-by: Steven Rostedt 
Signed-off-by: Greg Kroah-Hartman

cgroup: cgroup_subsys->fork() should be called after the task is added to css_set

2014-03-11T23:10:03+00:00

commit 5edee61edeaaebafe584f8fb7074c1ef4658596b upstream.

cgroup core has a bug which violates a basic rule about event
notifications - when a new entity needs to be added, you add that to
the notification list first and then make the new entity conform to
the current state.  If done in the reverse order, an event happening
inbetween will be lost.

cgroup_subsys->fork() is invoked way before the new task is added to
the css_set.  Currently, cgroup_freezer is the only user of ->fork()
and uses it to make new tasks conform to the current state of the
freezer.  If FROZEN state is requested while fork is in progress
between cgroup_fork_callbacks() and cgroup_post_fork(), the child
could escape freezing - the cgroup isn't frozen when ->fork() is
called and the freezer couldn't see the new task on the css_set.

This patch moves cgroup_subsys->fork() invocation to
cgroup_post_fork() after the new task is added to the css_set.
cgroup_fork_callbacks() is removed.

Because now a task may be migrated during cgroup_subsys->fork(),
freezer_fork() is updated so that it adheres to the usual RCU locking
and the rather pointless comment on why locking can be different there
is removed (if it doesn't make anything simpler, why even bother?).

Signed-off-by: Tejun Heo 
Cc: Oleg Nesterov 
Cc: Rafael J. Wysocki 
[hq: Backported to 3.4:
 - Adjust context
 - Iterate over first CGROUP_BUILTIN_SUBSYS_COUNT elements of subsys]
Signed-off-by: Qiang Huang 
Signed-off-by: Greg Kroah-Hartman

mm/fork: fix overflow in vma length when copying mmap on clone

2012-06-09T15:36:06+00:00

commit 7edc8b0ac16cbaed7cb4ea4c6b95ce98d2997e84 upstream.

The vma length in dup_mmap is calculated and stored in a unsigned int,
which is insufficient and hence overflows for very large maps (beyond
16TB). The following program demonstrates this:

#include 
#include 
#include 

#define GIG 1024 * 1024 * 1024L
#define EXTENT 16393

int main(void)
{
        int i, r;
        void *m;
        char buf[1024];

        for (i = 0; i < EXTENT; i++) {
                m = mmap(NULL, (size_t) 1 * 1024 * 1024 * 1024L,
                         PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);

                if (m == (void *)-1)
                        printf("MMAP Failed: %d\n", m);
                else
                        printf("%d : MMAP returned %p\n", i, m);

                r = fork();

                if (r == 0) {
                        printf("%d: successed\n", i);
                        return 0;
                } else if (r < 0)
                        printf("FORK Failed: %d\n", r);
                else if (r > 0)
                        wait(NULL);
        }
        return 0;
}

Increase the storage size of the result to unsigned long, which is
sufficient for storing the difference between addresses.

Signed-off-by: Siddhesh Poyarekar 
Cc: Tejun Heo 
Cc: Oleg Nesterov 
Cc: Jens Axboe 
Cc: Peter Zijlstra 
Acked-by: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

namespaces, pid_ns: fix leakage on fork() failure

2012-05-10T22:06:44+00:00

Fork() failure post namespace creation for a child cloned with
CLONE_NEWPID leaks pid_namespace/mnt_cache due to proc being mounted
during creation, but not unmounted during cleanup.  Call
pid_ns_release_proc() during cleanup.

Signed-off-by: Mike Galbraith 
Acked-by: Oleg Nesterov 
Reviewed-by: "Eric W. Biederman" 
Cc: Pavel Emelyanov 
Cc: Cyrill Gorcunov 
Cc: Louis Rilling 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

prctl: add PR_{SET,GET}_CHILD_SUBREAPER to allow simple process supervision

2012-03-23T23:58:32+00:00

Userspace service managers/supervisors need to track their started
services.  Many services daemonize by double-forking and get implicitly
re-parented to PID 1.  The service manager will no longer be able to
receive the SIGCHLD signals for them, and is no longer in charge of
reaping the children with wait().  All information about the children is
lost at the moment PID 1 cleans up the re-parented processes.

With this prctl, a service manager process can mark itself as a sort of
'sub-init', able to stay as the parent for all orphaned processes
created by the started services.  All SIGCHLD signals will be delivered
to the service manager.

Receiving SIGCHLD and doing wait() is in cases of a service-manager much
preferred over any possible asynchronous notification about specific
PIDs, because the service manager has full access to the child process
data in /proc and the PID can not be re-used until the wait(), the
service-manager itself is in charge of, has happened.

As a side effect, the relevant parent PID information does not get lost
by a double-fork, which results in a more elaborate process tree and
'ps' output:

before:
  # ps afx
  253 ?        Ss     0:00 /bin/dbus-daemon --system --nofork
  294 ?        Sl     0:00 /usr/libexec/polkit-1/polkitd
  328 ?        S      0:00 /usr/sbin/modem-manager
  608 ?        Sl     0:00 /usr/libexec/colord
  658 ?        Sl     0:00 /usr/libexec/upowerd
  819 ?        Sl     0:00 /usr/libexec/imsettings-daemon
  916 ?        Sl     0:00 /usr/libexec/udisks-daemon
  917 ?        S      0:00  \_ udisks-daemon: not polling any devices

after:
  # ps afx
  294 ?        Ss     0:00 /bin/dbus-daemon --system --nofork
  426 ?        Sl     0:00  \_ /usr/libexec/polkit-1/polkitd
  449 ?        S      0:00  \_ /usr/sbin/modem-manager
  635 ?        Sl     0:00  \_ /usr/libexec/colord
  705 ?        Sl     0:00  \_ /usr/libexec/upowerd
  959 ?        Sl     0:00  \_ /usr/libexec/udisks-daemon
  960 ?        S      0:00  |   \_ udisks-daemon: not polling any devices
  977 ?        Sl     0:00  \_ /usr/libexec/packagekitd

This prctl is orthogonal to PID namespaces.  PID namespaces are isolated
from each other, while a service management process usually requires the
services to live in the same namespace, to be able to talk to each
other.

Users of this will be the systemd per-user instance, which provides
init-like functionality for the user's login session and D-Bus, which
activates bus services on-demand.  Both need init-like capabilities to
be able to properly keep track of the services they start.

Many thanks to Oleg for several rounds of review and insights.

[akpm@linux-foundation.org: fix comment layout and spelling]
[akpm@linux-foundation.org: add lengthy code comment from Oleg]
Reviewed-by: Oleg Nesterov 
Signed-off-by: Lennart Poettering 
Signed-off-by: Kay Sievers 
Acked-by: Valdis Kletnieks 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'akpm' (Andrew's patch-bomb)

2012-03-22T16:04:48+00:00

Merge first batch of patches from Andrew Morton:
 "A few misc things and all the MM queue"

* emailed from Andrew Morton : (92 commits)
  memcg: avoid THP split in task migration
  thp: add HPAGE_PMD_* definitions for !CONFIG_TRANSPARENT_HUGEPAGE
  memcg: clean up existing move charge code
  mm/memcontrol.c: remove unnecessary 'break' in mem_cgroup_read()
  mm/memcontrol.c: remove redundant BUG_ON() in mem_cgroup_usage_unregister_event()
  mm/memcontrol.c: s/stealed/stolen/
  memcg: fix performance of mem_cgroup_begin_update_page_stat()
  memcg: remove PCG_FILE_MAPPED
  memcg: use new logic for page stat accounting
  memcg: remove PCG_MOVE_LOCK flag from page_cgroup
  memcg: simplify move_account() check
  memcg: remove EXPORT_SYMBOL(mem_cgroup_update_page_stat)
  memcg: kill dead prev_priority stubs
  memcg: remove PCG_CACHE page_cgroup flag
  memcg: let css_get_next() rely upon rcu_read_lock()
  cgroup: revert ss_id_lock to spinlock
  idr: make idr_get_next() good for rcu_read_lock()
  memcg: remove unnecessary thp check in page stat accounting
  memcg: remove redundant returns
  memcg: enum lru_list lru
  ...

cpuset: mm: reduce large amounts of memory barrier related damage v3

2012-03-22T00:54:59+00:00

Commit c0ff7453bb5c ("cpuset,mm: fix no node to alloc memory when
changing cpuset's mems") wins a super prize for the largest number of
memory barriers entered into fast paths for one commit.

[get|put]_mems_allowed is incredibly heavy with pairs of full memory
barriers inserted into a number of hot paths.  This was detected while
investigating at large page allocator slowdown introduced some time
after 2.6.32.  The largest portion of this overhead was shown by
oprofile to be at an mfence introduced by this commit into the page
allocator hot path.

For extra style points, the commit introduced the use of yield() in an
implementation of what looks like a spinning mutex.

This patch replaces the full memory barriers on both read and write
sides with a sequence counter with just read barriers on the fast path
side.  This is much cheaper on some architectures, including x86.  The
main bulk of the patch is the retry logic if the nodemask changes in a
manner that can cause a false failure.

While updating the nodemask, a check is made to see if a false failure
is a risk.  If it is, the sequence number gets bumped and parallel
allocators will briefly stall while the nodemask update takes place.

In a page fault test microbenchmark, oprofile samples from
__alloc_pages_nodemask went from 4.53% of all samples to 1.15%.  The
actual results were

                             3.3.0-rc3          3.3.0-rc3
                             rc3-vanilla        nobarrier-v2r1
    Clients   1 UserTime       0.07 (  0.00%)   0.08 (-14.19%)
    Clients   2 UserTime       0.07 (  0.00%)   0.07 (  2.72%)
    Clients   4 UserTime       0.08 (  0.00%)   0.07 (  3.29%)
    Clients   1 SysTime        0.70 (  0.00%)   0.65 (  6.65%)
    Clients   2 SysTime        0.85 (  0.00%)   0.82 (  3.65%)
    Clients   4 SysTime        1.41 (  0.00%)   1.41 (  0.32%)
    Clients   1 WallTime       0.77 (  0.00%)   0.74 (  4.19%)
    Clients   2 WallTime       0.47 (  0.00%)   0.45 (  3.73%)
    Clients   4 WallTime       0.38 (  0.00%)   0.37 (  1.58%)
    Clients   1 Flt/sec/cpu  497620.28 (  0.00%) 520294.53 (  4.56%)
    Clients   2 Flt/sec/cpu  414639.05 (  0.00%) 429882.01 (  3.68%)
    Clients   4 Flt/sec/cpu  257959.16 (  0.00%) 258761.48 (  0.31%)
    Clients   1 Flt/sec      495161.39 (  0.00%) 517292.87 (  4.47%)
    Clients   2 Flt/sec      820325.95 (  0.00%) 850289.77 (  3.65%)
    Clients   4 Flt/sec      1020068.93 (  0.00%) 1022674.06 (  0.26%)
    MMTests Statistics: duration
    Sys Time Running Test (seconds)             135.68    132.17
    User+Sys Time Running Test (seconds)         164.2    160.13
    Total Elapsed Time (seconds)                123.46    120.87

The overall improvement is small but the System CPU time is much
improved and roughly in correlation to what oprofile reported (these
performance figures are without profiling so skew is expected).  The
actual number of page faults is noticeably improved.

For benchmarks like kernel builds, the overall benefit is marginal but
the system CPU time is slightly reduced.

To test the actual bug the commit fixed I opened two terminals.  The
first ran within a cpuset and continually ran a small program that
faulted 100M of anonymous data.  In a second window, the nodemask of the
cpuset was continually randomised in a loop.

Without the commit, the program would fail every so often (usually
within 10 seconds) and obviously with the commit everything worked fine.
With this patch applied, it also worked fine so the fix should be
functionally equivalent.

Signed-off-by: Mel Gorman 
Cc: Miao Xie 
Cc: David Rientjes 
Cc: Peter Zijlstra 
Cc: Christoph Lameter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds