linux-stable.git/kernel/rcu/tree.c, branch v6.1.35

rcu/kvfree: Avoid freeing new kfree_rcu() memory after old grace period

2023-06-21T14:01:02+00:00

commit 5da7cb193db32da783a3f3e77d8b639989321d48 upstream.

Memory passed to kvfree_rcu() that is to be freed is tracked by a
per-CPU kfree_rcu_cpu structure, which in turn contains pointers
to kvfree_rcu_bulk_data structures that contain pointers to memory
that has not yet been handed to RCU, along with an kfree_rcu_cpu_work
structure that tracks the memory that has already been handed to RCU.
These structures track three categories of memory: (1) Memory for
kfree(), (2) Memory for kvfree(), and (3) Memory for both that arrived
during an OOM episode.  The first two categories are tracked in a
cache-friendly manner involving a dynamically allocated page of pointers
(the aforementioned kvfree_rcu_bulk_data structures), while the third
uses a simple (but decidedly cache-unfriendly) linked list through the
rcu_head structures in each block of memory.

On a given CPU, these three categories are handled as a unit, with that
CPU's kfree_rcu_cpu_work structure having one pointer for each of the
three categories.  Clearly, new memory for a given category cannot be
placed in the corresponding kfree_rcu_cpu_work structure until any old
memory has had its grace period elapse and thus has been removed.  And
the kfree_rcu_monitor() function does in fact check for this.

Except that the kfree_rcu_monitor() function checks these pointers one
at a time.  This means that if the previous kfree_rcu() memory passed
to RCU had only category 1 and the current one has only category 2, the
kfree_rcu_monitor() function will send that current category-2 memory
along immediately.  This can result in memory being freed too soon,
that is, out from under unsuspecting RCU readers.

To see this, consider the following sequence of events, in which:

o	Task A on CPU 0 calls rcu_read_lock(), then uses "from_cset",
	then is preempted.

o	CPU 1 calls kfree_rcu(cset, rcu_head) in order to free "from_cset"
	after a later grace period.  Except that "from_cset" is freed
	right after the previous grace period ended, so that "from_cset"
	is immediately freed.  Task A resumes and references "from_cset"'s
	member, after which nothing good happens.

In full detail:

CPU 0					CPU 1
----------------------			----------------------
count_memcg_event_mm()
|rcu_read_lock()  <---
|mem_cgroup_from_task()
 |// css_set_ptr is the "from_cset" mentioned on CPU 1
 |css_set_ptr = rcu_dereference((task)->cgroups)
 |// Hard irq comes, current task is scheduled out.

					cgroup_attach_task()
					|cgroup_migrate()
					|cgroup_migrate_execute()
					|css_set_move_task(task, from_cset, to_cset, true)
					|cgroup_move_task(task, to_cset)
					|rcu_assign_pointer(.., to_cset)
					|...
					|cgroup_migrate_finish()
					|put_css_set_locked(from_cset)
					|from_cset->refcount return 0
					|kfree_rcu(cset, rcu_head) // free from_cset after new gp
					|add_ptr_to_bulk_krc_lock()
					|schedule_delayed_work(&krcp->monitor_work, ..)

					kfree_rcu_monitor()
					|krcp->bulk_head[0]'s work attached to krwp->bulk_head_free[]
					|queue_rcu_work(system_wq, &krwp->rcu_work)
					|if rwork->rcu.work is not in WORK_STRUCT_PENDING_BIT state,
					|call_rcu(&rwork->rcu, rcu_work_rcufn) <--- request new gp

					// There is a perious call_rcu(.., rcu_work_rcufn)
					// gp end, rcu_work_rcufn() is called.
					rcu_work_rcufn()
					|__queue_work(.., rwork->wq, &rwork->work);

					|kfree_rcu_work()
					|krwp->bulk_head_free[0] bulk is freed before new gp end!!!
					|The "from_cset" is freed before new gp end.

// the task resumes some time later.
 |css_set_ptr->subsys[(subsys_id) <--- Caused kernel crash, because css_set_ptr is freed.

This commit therefore causes kfree_rcu_monitor() to refrain from moving
kfree_rcu() memory to the kfree_rcu_cpu_work structure until the RCU
grace period has completed for all three categories.

v2: Use helper function instead of inserted code block at kfree_rcu_monitor().

Fixes: 34c881745549 ("rcu: Support kfree_bulk() interface in kfree_rcu()")
Fixes: 5f3c8d620447 ("rcu/tree: Maintain separate array for vmalloc ptrs")
Reported-by: Mukesh Ojha 
Signed-off-by: Ziwei Dai 
Reviewed-by: Uladzislau Rezki (Sony) 
Tested-by: Uladzislau Rezki (Sony) 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Greg Kroah-Hartman

rcu: Avoid stack overflow due to __rcu_irq_enter_check_tick() being kprobe-ed

2023-05-11T14:03:02+00:00

commit 7a29fb4a4771124bc61de397dbfc1554dbbcc19c upstream.

Registering a kprobe on __rcu_irq_enter_check_tick() can cause kernel
stack overflow as shown below. This issue can be reproduced by enabling
CONFIG_NO_HZ_FULL and booting the kernel with argument "nohz_full=",
and then giving the following commands at the shell prompt:

  # cd /sys/kernel/tracing/
  # echo 'p:mp1 __rcu_irq_enter_check_tick' >> kprobe_events
  # echo 1 > events/kprobes/enable

This commit therefore adds __rcu_irq_enter_check_tick() to the kprobes
blacklist using NOKPROBE_SYMBOL().

Insufficient stack space to handle exception!
ESR: 0x00000000f2000004 -- BRK (AArch64)
FAR: 0x0000ffffccf3e510
Task stack:     [0xffff80000ad30000..0xffff80000ad38000]
IRQ stack:      [0xffff800008050000..0xffff800008058000]
Overflow stack: [0xffff089c36f9f310..0xffff089c36fa0310]
CPU: 5 PID: 190 Comm: bash Not tainted 6.2.0-rc2-00320-g1f5abbd77e2c #19
Hardware name: linux,dummy-virt (DT)
pstate: 400003c5 (nZcv DAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __rcu_irq_enter_check_tick+0x0/0x1b8
lr : ct_nmi_enter+0x11c/0x138
sp : ffff80000ad30080
x29: ffff80000ad30080 x28: ffff089c82e20000 x27: 0000000000000000
x26: 0000000000000000 x25: ffff089c02a8d100 x24: 0000000000000000
x23: 00000000400003c5 x22: 0000ffffccf3e510 x21: ffff089c36fae148
x20: ffff80000ad30120 x19: ffffa8da8fcce148 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: ffffa8da8e44ea6c
x14: ffffa8da8e44e968 x13: ffffa8da8e03136c x12: 1fffe113804d6809
x11: ffff6113804d6809 x10: 0000000000000a60 x9 : dfff800000000000
x8 : ffff089c026b404f x7 : 00009eec7fb297f7 x6 : 0000000000000001
x5 : ffff80000ad30120 x4 : dfff800000000000 x3 : ffffa8da8e3016f4
x2 : 0000000000000003 x1 : 0000000000000000 x0 : 0000000000000000
Kernel panic - not syncing: kernel stack overflow
CPU: 5 PID: 190 Comm: bash Not tainted 6.2.0-rc2-00320-g1f5abbd77e2c #19
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0xf8/0x108
 show_stack+0x20/0x30
 dump_stack_lvl+0x68/0x84
 dump_stack+0x1c/0x38
 panic+0x214/0x404
 add_taint+0x0/0xf8
 panic_bad_stack+0x144/0x160
 handle_bad_stack+0x38/0x58
 __bad_stack+0x78/0x7c
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 [...]
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 arm64_enter_el1_dbg.isra.0+0x14/0x20
 el1_dbg+0x2c/0x90
 el1h_64_sync_handler+0xcc/0xe8
 el1h_64_sync+0x64/0x68
 __rcu_irq_enter_check_tick+0x0/0x1b8
 el1_interrupt+0x28/0x60
 el1h_64_irq_handler+0x18/0x28
 el1h_64_irq+0x64/0x68
 __ftrace_set_clr_event_nolock+0x98/0x198
 __ftrace_set_clr_event+0x58/0x80
 system_enable_write+0x144/0x178
 vfs_write+0x174/0x738
 ksys_write+0xd0/0x188
 __arm64_sys_write+0x4c/0x60
 invoke_syscall+0x64/0x180
 el0_svc_common.constprop.0+0x84/0x160
 do_el0_svc+0x48/0xe8
 el0_svc+0x34/0xd0
 el0t_64_sync_handler+0xb8/0xc0
 el0t_64_sync+0x190/0x194
SMP: stopping secondary CPUs
Kernel Offset: 0x28da86000000 from 0xffff800008000000
PHYS_OFFSET: 0xfffff76600000000
CPU features: 0x00000,01a00100,0000421b
Memory Limit: none

Acked-by: Joel Fernandes (Google) 
Link: https://lore.kernel.org/all/20221119040049.795065-1-zhengyejian1@huawei.com/
Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()")
Signed-off-by: Zheng Yejian 
Cc: stable@vger.kernel.org
Signed-off-by: Paul E. McKenney 
Signed-off-by: Joel Fernandes (Google) 
Signed-off-by: Greg Kroah-Hartman

rcu: Fix __this_cpu_read() lockdep warning in rcu_force_quiescent_state()

2022-12-31T12:32:56+00:00

[ Upstream commit ceb1c8c9b8aa9199da46a0f29d2d5f08d9b44c15 ]

Running rcutorture with non-zero fqs_duration module parameter in a
kernel built with CONFIG_PREEMPTION=y results in the following splat:

BUG: using __this_cpu_read() in preemptible [00000000]
code: rcu_torture_fqs/398
caller is __this_cpu_preempt_check+0x13/0x20
CPU: 3 PID: 398 Comm: rcu_torture_fqs Not tainted 6.0.0-rc1-yoctodev-standard+
Call Trace:

dump_stack_lvl+0x5b/0x86
dump_stack+0x10/0x16
check_preemption_disabled+0xe5/0xf0
__this_cpu_preempt_check+0x13/0x20
rcu_force_quiescent_state.part.0+0x1c/0x170
rcu_force_quiescent_state+0x1e/0x30
rcu_torture_fqs+0xca/0x160
? rcu_torture_boost+0x430/0x430
kthread+0x192/0x1d0
? kthread_complete_and_exit+0x30/0x30
ret_from_fork+0x22/0x30


The problem is that rcu_force_quiescent_state() uses __this_cpu_read()
in preemptible code instead of the proper raw_cpu_read().  This commit
therefore changes __this_cpu_read() to raw_cpu_read().

Signed-off-by: Zqiang 
Reviewed-by: Joel Fernandes (Google) 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Sasha Levin

rcu: Keep synchronize_rcu() from enabling irqs in early boot

2022-10-20T22:34:49+00:00

Making polled RCU grace periods account for expedited grace periods
required acquiring the leaf rcu_node structure's lock during early boot,
but after rcu_init() was called.  This lock is irq-disabled, but the
code incorrectly assumes that irqs are always disabled when invoking
synchronize_rcu().  The exception is early boot before the scheduler has
started, which means that upon return from synchronize_rcu(), irqs will
be incorrectly enabled.

This commit fixes this bug by using irqsave/irqrestore locking primitives.

Fixes: bf95b2bc3e42 ("rcu: Switch polled grace-period APIs to ->gp_seq_polled")

Reported-by: Steven Rostedt 
Signed-off-by: Paul E. McKenney

Merge branches 'doc.2022.08.31b', 'fixes.2022.08.31b', 'kvfree.2022.08.31b', 'nocb.2022.09.01a', 'poll.2022.08.31b', 'poll-srcu.2022.08.31b' and 'tasks.2022.08.31b' into HEAD

2022-09-01T17:55:57+00:00

doc.2022.08.31b: Documentation updates
fixes.2022.08.31b: Miscellaneous fixes
kvfree.2022.08.31b: kvfree_rcu() updates
nocb.2022.09.01a: NOCB CPU updates
poll.2022.08.31b: Full-oldstate RCU polling grace-period API
poll-srcu.2022.08.31b: Polled SRCU grace-period updates
tasks.2022.08.31b: Tasks RCU updates

rcu-tasks: Make RCU Tasks Trace check for userspace execution

2022-08-31T12:10:55+00:00

Userspace execution is a valid quiescent state for RCU Tasks Trace,
but the scheduling-clock interrupt does not currently report such
quiescent states.

Of course, the scheduling-clock interrupt is not strictly speaking
userspace execution.  However, the only way that this code is not
in a quiescent state is if something invoked rcu_read_lock_trace(),
and that would be reflected in the ->trc_reader_nesting field in
the task_struct structure.  Furthermore, this field is checked by
rcu_tasks_trace_qs(), which is invoked by rcu_tasks_qs() which is in
turn invoked by rcu_note_voluntary_context_switch() in kernels building
at least one of the RCU Tasks flavors.  It is therefore safe to invoke
rcu_tasks_trace_qs() from the rcu_sched_clock_irq().

But rcu_tasks_qs() also invokes rcu_tasks_classic_qs() for RCU
Tasks, which lacks the read-side markers provided by RCU Tasks Trace.
This raises the possibility that an RCU Tasks grace period could start
after the interrupt from userspace execution, but before the call to
rcu_sched_clock_irq().  However, it turns out that this is safe because
the RCU Tasks grace period waits for an RCU grace period, which will
wait for the entire scheduling-clock interrupt handler, including any
RCU Tasks read-side critical section that this handler might contain.

This commit therefore updates the rcu_sched_clock_irq() function's
check for usermode execution and its call to rcu_tasks_classic_qs()
to instead check for both usermode execution and interrupt from idle,
and to instead call rcu_note_voluntary_context_switch().  This
consolidates code and provides more faster RCU Tasks Trace
reporting of quiescent states in kernels that do scheduling-clock
interrupts for userspace execution.

[ paulmck: Consolidate checks into rcu_sched_clock_irq(). ]

Signed-off-by: Zqiang 
Signed-off-by: Paul E. McKenney

rcu: Make synchronize_rcu() fastpath update only boot-CPU counters

2022-08-31T12:09:22+00:00

Large systems can have hundreds of rcu_node structures, and updating
counters in each of them might slow down booting.  This commit therefore
updates only the counters in those rcu_node structures corresponding
to the boot CPU, up to and including the root rcu_node structure.

The counters for the remaining rcu_node structures are updated by the
rcu_scheduler_starting() function, which executes just before the first
non-boot kthread is spawned.

Signed-off-by: Paul E. McKenney

rcu: Remove ->rgos_polled field from rcu_gp_oldstate structure

2022-08-31T12:09:21+00:00

Because both normal and expedited grace periods increment their respective
counters on their pre-scheduler early boot fastpaths, the rcu_gp_oldstate
structure no longer needs its ->rgos_polled field.  This commit therefore
removes this field, shrinking this structure so that it is the same size
as an rcu_head structure.

Signed-off-by: Paul E. McKenney

rcu: Make synchronize_rcu() fast path update ->gp_seq counters

2022-08-31T12:09:21+00:00

This commit causes the early boot single-CPU synchronize_rcu() fastpath to
update the rcu_state and rcu_node structures' ->gp_seq and ->gp_seq_needed
counters.  This will allow the full-state polled grace-period APIs to
detect all normal grace periods without the need to track the special
combined polling-only counter, which is a step towards removing the
->rgos_polled field from the rcu_gp_oldstate, thereby reducing its size
by one third.

Signed-off-by: Paul E. McKenney

rcu-tasks: Remove grace-period fast-path rcu-tasks helper

2022-08-31T12:08:08+00:00

Now that the grace-period fast path can only happen during the
pre-scheduler portion of early boot, this fast path can no longer block
run-time RCU Tasks and RCU Tasks Trace grace periods.  This commit
therefore removes the conditional cond_resched_tasks_rcu_qs() invocation.

Signed-off-by: Paul E. McKenney