linux.git/init/init_task.c, branch v6.6.132

rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks

2024-11-08T15:28:22+00:00

[ Upstream commit 46faf9d8e1d52e4a91c382c6c72da6bd8e68297b ]

Holding a mutex across synchronize_rcu_tasks() and acquiring
that same mutex in code called from do_exit() after its call to
exit_tasks_rcu_start() but before its call to exit_tasks_rcu_stop()
results in deadlock.  This is by design, because tasks that are far
enough into do_exit() are no longer present on the tasks list, making
it a bit difficult for RCU Tasks to find them, let alone wait on them
to do a voluntary context switch.  However, such deadlocks are becoming
more frequent.  In addition, lockdep currently does not detect such
deadlocks and they can be difficult to reproduce.

In addition, if a task voluntarily context switches during that time
(for example, if it blocks acquiring a mutex), then this task is in an
RCU Tasks quiescent state.  And with some adjustments, RCU Tasks could
just as well take advantage of that fact.

This commit therefore initializes the data structures that will be needed
to rely on these quiescent states and to eliminate these deadlocks.

Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/

Reported-by: Chen Zhongjin 
Reported-by: Yang Jihong 
Signed-off-by: Paul E. McKenney 
Tested-by: Yang Jihong 
Tested-by: Chen Zhongjin 
Reviewed-by: Frederic Weisbecker 
Signed-off-by: Boqun Feng 
Stable-dep-of: fd70e9f1d85f ("rcu-tasks: Fix access non-existent percpu rtpcp variable in rcu_tasks_need_gpcb()")
Signed-off-by: Sasha Levin

rcu-tasks: Add data structures for lightweight grace periods

2022-06-20T16:22:28+00:00

This commit adds fields to task_struct and to rcu_tasks_percpu that will
be used to avoid the task-list scan for RCU Tasks Trace grace periods,
and also initializes these fields.

Signed-off-by: Paul E. McKenney 
Cc: Neeraj Upadhyay 
Cc: Eric Dumazet 
Cc: Alexei Starovoitov 
Cc: Andrii Nakryiko 
Cc: Martin KaFai Lau 
Cc: KP Singh

kcsan: Remove redundant zero-initialization of globals

2021-12-10T00:42:26+00:00

They are implicitly zero-initialized, remove explicit initialization.
It keeps the upcoming additions to kcsan_ctx consistent with the rest.

No functional change intended.

Signed-off-by: Marco Elver 
Acked-by: Mark Rutland 
Signed-off-by: Paul E. McKenney

sched: Introduce task_struct::user_cpus_ptr to track requested affinity

2021-08-20T10:33:00+00:00

In preparation for saving and restoring the user-requested CPU affinity
mask of a task, add a new cpumask_t pointer to 'struct task_struct'.

If the pointer is non-NULL, then the mask is copied across fork() and
freed on task exit.

Signed-off-by: Will Deacon 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Valentin Schneider 
Link: https://lore.kernel.org/r/20210730112443.23245-7-will@kernel.org

sched: Change task_struct::state

2021-06-18T09:43:09+00:00

Change the type and name of task_struct::state. Drop the volatile and
shrink it to an 'unsigned int'. Rename it in order to find all uses
such that we can use READ_ONCE/WRITE_ONCE as appropriate.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Daniel Bristot de Oliveira 
Acked-by: Will Deacon 
Acked-by: Daniel Thompson 
Link: https://lore.kernel.org/r/20210611082838.550736351@infradead.org

seccomp: Fix CONFIG tests for Seccomp_filters

2021-03-31T05:33:50+00:00

Strictly speaking, seccomp filters are only used
when CONFIG_SECCOMP_FILTER.
This patch fixes the condition to enable "Seccomp_filters"
in /proc/$pid/status.

Signed-off-by: Kenta Tada 
Fixes: c818c03b661c ("seccomp: Report number of loaded filters in /proc/$pid/status")
Signed-off-by: Kees Cook 
Link: https://lore.kernel.org/r/OSBPR01MB26772D245E2CF4F26B76A989F5669@OSBPR01MB2677.jpnprd01.prod.outlook.com

fgraph: Initialize tracing_graph_pause at task creation

2021-01-29T20:07:32+00:00

On some archs, the idle task can call into cpu_suspend(). The cpu_suspend()
will disable or pause function graph tracing, as there's some paths in
bringing down the CPU that can have issues with its return address being
modified. The task_struct structure has a "tracing_graph_pause" atomic
counter, that when set to something other than zero, the function graph
tracer will not modify the return address.

The problem is that the tracing_graph_pause counter is initialized when the
function graph tracer is enabled. This can corrupt the counter for the idle
task if it is suspended in these architectures.

   CPU 1				CPU 2
   -----				-----
  do_idle()
    cpu_suspend()
      pause_graph_tracing()
          task_struct->tracing_graph_pause++ (0 -> 1)

				start_graph_tracing()
				  for_each_online_cpu(cpu) {
				    ftrace_graph_init_idle_task(cpu)
				      task-struct->tracing_graph_pause = 0 (1 -> 0)

      unpause_graph_tracing()
          task_struct->tracing_graph_pause-- (0 -> -1)

The above should have gone from 1 to zero, and enabled function graph
tracing again. But instead, it is set to -1, which keeps it disabled.

There's no reason that the field tracing_graph_pause on the task_struct can
not be initialized at boot up.

Cc: stable@vger.kernel.org
Fixes: 380c4b1411ccd ("tracing/function-graph-tracer: append the tracing_graph_flag")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211339
Reported-by: pierre.gondois@arm.com
Signed-off-by: Steven Rostedt (VMware)

kasan, arm64: only use kasan_depth for software modes

2020-12-22T20:55:07+00:00

This is a preparatory commit for the upcoming addition of a new hardware
tag-based (MTE-based) KASAN mode.

Hardware tag-based KASAN won't use kasan_depth.  Only define and use it
when one of the software KASAN modes are enabled.

No functional changes for software modes.

Link: https://lkml.kernel.org/r/e16f15aeda90bc7fb4dfc2e243a14b74cc5c8219.1606161801.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Signed-off-by: Vincenzo Frascino 
Reviewed-by: Catalin Marinas 
Reviewed-by: Alexander Potapenko 
Tested-by: Vincenzo Frascino 
Cc: Andrey Ryabinin 
Cc: Branislav Rankov 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Kevin Brodsky 
Cc: Marco Elver 
Cc: Vasily Gorbik 
Cc: Will Deacon 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

exec: Transform exec_update_mutex into a rw_semaphore

2020-12-10T19:13:32+00:00

Recently syzbot reported[0] that there is a deadlock amongst the users
of exec_update_mutex.  The problematic lock ordering found by lockdep
was:

   perf_event_open  (exec_update_mutex -> ovl_i_mutex)
   chown            (ovl_i_mutex       -> sb_writes)
   sendfile         (sb_writes         -> p->lock)
     by reading from a proc file and writing to overlayfs
   proc_pid_syscall (p->lock           -> exec_update_mutex)

While looking at possible solutions it occured to me that all of the
users and possible users involved only wanted to state of the given
process to remain the same.  They are all readers.  The only writer is
exec.

There is no reason for readers to block on each other.  So fix
this deadlock by transforming exec_update_mutex into a rw_semaphore
named exec_update_lock that only exec takes for writing.

Cc: Jann Horn 
Cc: Vasiliy Kulikov 
Cc: Al Viro 
Cc: Bernd Edlinger 
Cc: Oleg Nesterov 
Cc: Christopher Yeoh 
Cc: Cyrill Gorcunov 
Cc: Sargun Dhillon 
Cc: Christian Brauner 
Cc: Arnd Bergmann 
Cc: Peter Zijlstra 
Cc: Ingo Molnar 
Cc: Arnaldo Carvalho de Melo 
Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex")
[0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman

io_uring: don't rely on weak ->files references

2020-10-01T02:32:32+00:00

Grab actual references to the files_struct. To avoid circular references
issues due to this, we add a per-task note that keeps track of what
io_uring contexts a task has used. When the tasks execs or exits its
assigned files, we cancel requests based on this tracking.

With that, we can grab proper references to the files table, and no
longer need to rely on stashing away ring_fd and ring_file to check
if the ring_fd may have been closed.

Cc: stable@vger.kernel.org # v5.5+
Reviewed-by: Pavel Begunkov 
Signed-off-by: Jens Axboe