Proxmox-Port/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2025-08-15 14:37:33 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity
1,381,693 Commits 108 Branches 5,270 Tags 6.1 GiB
master
Commit Graph

9 Commits

Author SHA1 Message Date
Steven Rostedt
b3b9cb11aa unwind: Finish up unwind when a task exits 
On do_exit() when a task is exiting, if a unwind is requested and the
deferred user stacktrace is deferred via the task_work, the task_work
callback is called after exit_mm() is called in do_exit(). This means that
the user stack trace will not be retrieved and an empty stack is created.

Instead, add a function unwind_deferred_task_exit() and call it just
before exit_mm() so that the unwinder can call the requested callbacks
with the user space stack.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182406.504259474@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:11 -04:00
Steven Rostedt
357eda2d74 unwind deferred: Use SRCU unwind_deferred_task_work() 
Instead of using the callback_mutex to protect the link list of callbacks
in unwind_deferred_task_work(), use SRCU instead. This gets called every
time a task exits that has to record a stack trace that was requested.
This can happen for many tasks on several CPUs at the same time. A mutex
is a bottleneck and can cause a bit of contention and slow down performance.

As the callbacks themselves are allowed to sleep, regular RCU cannot be
used to protect the list. Instead use SRCU, as that still allows the
callbacks to sleep and the list can be read without needing to hold the
callback_mutex.

Link: https://lore.kernel.org/all/ca9bd83a-6c80-4ee0-a83c-224b9d60b755@efficios.com/

Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182406.331548065@kernel.org
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:11 -04:00
Steven Rostedt
858fa8a3b0 unwind: Add USED bit to only have one conditional on way back to user space 
On the way back to user space, the function unwind_reset_info() is called
unconditionally (but always inlined). It currently has two conditionals.
One that checks the unwind_mask which is set whenever a deferred trace is
called and is used to know that the mask needs to be cleared. The other
checks if the cache has been allocated, and if so, it resets the
nr_entries so that the unwinder knows it needs to do the work to get a new
user space stack trace again (it only does it once per entering the
kernel).

Use one of the bits in the unwind mask as a "USED" bit that gets set
whenever a trace is created. This will make it possible to only check the
unwind_mask in the unwind_reset_info() to know if it needs to do work or
not and eliminates a conditional that happens every time the task goes
back to user space.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182406.155422551@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:11 -04:00
Steven Rostedt
4c75133e74 unwind deferred: Add unwind_completed mask to stop spurious callbacks 
If there's more than one registered tracer to the unwind deferred
infrastructure, it is currently possible that one tracer could cause extra
callbacks to happen for another tracer if the former requests a deferred
stacktrace after the latter's callback was executed and before the task
went back to user space.

Here's an example of how this could occur:

  [Task enters kernel]
    tracer 1 request -> add cookie to its buffer
    tracer 1 request -> add cookie to its buffer
    <..>
    [ task work executes ]
    tracer 1 callback -> add trace + cookie to its buffer

    [tracer 2 requests and triggers the task work again]
    [ task work executes again ]
    tracer 1 callback -> add trace + cookie to its buffer
    tracer 2 callback -> add trace + cookie to its buffer
 [Task exits back to user space]

This is because the bit for tracer 1 gets set in the task's unwind_mask
when it did its request and does not get cleared until the task returns
back to user space. But if another tracer were to request another deferred
stacktrace, then the next task work will executed all tracer's callbacks
that have their bits set in the task's unwind_mask.

To fix this issue, add another mask called unwind_completed and place it
into the task's info->cache structure. The cache structure is allocated
on the first occurrence of a deferred stacktrace and this unwind_completed
mask is not needed until then. It's better to have it in the cache than to
permanently waste space in the task_struct.

After a tracer's callback is executed, it's bit gets set in this
unwind_completed mask. When the task_work enters, it will AND the task's
unwind_mask with the inverse of the unwind_completed which will eliminate
any work that already had its callback executed since the task entered the
kernel.

When the task leaves the kernel, it will reset this unwind_completed mask
just like it resets the other values as it enters user space.

Link: https://lore.kernel.org/all/20250716142609.47f0e4a5@batman.local.home/

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.989222722@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:10 -04:00
Steven Rostedt
be3d526a5b unwind deferred: Use bitmask to determine which callbacks to call 
In order to know which registered callback requested a stacktrace for when
the task goes back to user space, add a bitmask to keep track of all
registered tracers. The bitmask is the size of long, which means that on a
32 bit machine, it can have at most 32 registered tracers, and on 64 bit,
it can have at most 64 registered tracers. This should not be an issue as
there should not be more than 10 (unless BPF can abuse this?).

When a tracer registers with unwind_deferred_init() it will get a bit
number assigned to it. When a tracer requests a stacktrace, it will have
its bit set within the task_struct. When the task returns back to user
space, it will call the callbacks for all the registered tracers where
their bits are set in the task's mask.

When a tracer is removed by the unwind_deferred_cancel() all current tasks
will clear the associated bit, just in case another tracer gets registered
immediately afterward and then gets their callback called unexpectedly.

To prevent live locks from happening if an event that happens between the
task_work and when the task goes back to user space, triggers the deferred
unwind, have the unwind_mask get cleared on exit to user space and not
after the callback is made.

Move the pending bit from a value on the task_struct to bit zero of the
unwind_mask (saves space on the task_struct). This will allow modifying
the pending bit along with the work bits atomically.

Instead of clearing a work's bit after its callback is called, it is
delayed until exit. If the work is requested again, the task_work is not
queued again and the request will be notified that the task has already been
called by returning a positive number (the same as if it was already
pending).

The pending bit is cleared before calling the callback functions but the
current work bits remain. If one of the called works registers again, it
will not trigger a task_work if its bit is still present in the task's
unwind_mask.

If a new work requests a deferred unwind, then it will set both the
pending bit and its own bit. Note this will also cause any work that was
previously queued and had their callback already executed to be executed
again. Future work will remove these spurious callbacks.

The use of atomic_long bit operations were suggested by Peter Zijlstra:
Link: https://lore.kernel.org/all/20250715102912.GQ1613200@noisy.programming.kicks-ass.net/
The unwind_mask could not be converted to atomic_long_t do to atomic_long
not having all the bit operations needed by unwind_mask. Instead it
follows other use cases in the kernel and just typecasts the unwind_mask
to atomic_long_t when using the two atomic_long functions.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.822789300@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:10 -04:00
Steven Rostedt
055c7060e7 unwind_user/deferred: Make unwind deferral requests NMI-safe 
Make unwind_deferred_request() NMI-safe so tracers in NMI context can
call it and safely request a user space stacktrace when the task exits.

Note, this is only allowed for architectures that implement a safe
cmpxchg. If an architecture requests a deferred stack trace from NMI
context that does not support a safe NMI cmpxchg, it will get an -EINVAL
and trigger a warning. For those architectures, they would need another
method (perhaps an irqwork), to request a deferred user space stack trace.
That can be dealt with later if one of theses architectures require this
feature.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.657072238@kernel.org
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:10 -04:00
Josh Poimboeuf
2dffa355f6 unwind_user/deferred: Add deferred unwinding interface 
Add an interface for scheduling task work to unwind the user space stack
before returning to user space. This solves several problems for its
callers:

  - Ensure the unwind happens in task context even if the caller may be
    running in interrupt context.

  - Avoid duplicate unwinds, whether called multiple times by the same
    caller or by different callers.

  - Create a "context cookie" which allows trace post-processing to
    correlate kernel unwinds/traces with the user unwind.

A concept of a "cookie" is created to detect when the stacktrace is the
same. A cookie is generated the first time a user space stacktrace is
requested after the task enters the kernel. As the stacktrace is saved on
the task_struct while the task is in the kernel, if another request comes
in, if the cookie is still the same, it will use the saved stacktrace,
and not have to regenerate one.

The cookie is passed to the caller on request, and when the stacktrace is
generated upon returning to user space, it calls the requester's callback
with the cookie as well as the stacktrace. The cookie is cleared
when it goes back to user space. Note, this currently adds another
conditional to the unwind_reset_info() path that is always called
returning to user space, but future changes will put this back to a single
conditional.

A global list is created and protected by a global mutex that holds
tracers that register with the unwind infrastructure. The number of
registered tracers will be limited in future changes. Each perf program or
ftrace instance will register its own descriptor to use for deferred
unwind stack traces.

Note, in the function unwind_deferred_task_work() that gets called when
returning to user space, it uses a global mutex for synchronization which
will cause a big bottleneck. This will be replaced by SRCU, but that
change adds some complex synchronization that deservers its own commit.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Jens Remus <jremus@linux.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.488066537@kernel.org
Co-developed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:10 -04:00
Josh Poimboeuf
b9c7352410 unwind_user/deferred: Add unwind cache 
Cache the results of the unwind to ensure the unwind is only performed
once, even when called by multiple tracers.

The cache nr_entries gets cleared every time the task exits the kernel.
When a stacktrace is requested, nr_entries gets set to the number of
entries in the stacktrace. If another stacktrace is requested, if
nr_entries is not zero, then it contains the same stacktrace that would be
retrieved so it is not processed again and the entries is given to the
caller.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.319691167@kernel.org
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Reviewed-By: Indu Bhagat <indu.bhagat@oracle.com>
Co-developed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-31 10:20:04 -04:00
Steven Rostedt
5e32d0f15c unwind_user/deferred: Add unwind_user_faultable() 
Add a new API to retrieve a user space callstack called
unwind_user_faultable(). The difference between this user space stack
tracer from the current user space stack tracer is that this must be
called from faultable context as it may use routines to access user space
data that needs to be faulted in.

It can be safely called from entering or exiting a system call as the code
can still be faulted in there.

This code is based on work by Josh Poimboeuf's deferred unwinding code:

Link: https://lore.kernel.org/all/6052e8487746603bdb29b65f4033e739092d9925.1737511963.git.jpoimboe@kernel.org/

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Indu Bhagat <indu.bhagat@oracle.com>
Cc: "Jose E. Marchesi" <jemarch@gnu.org>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/20250729182405.147896868@kernel.org
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
 2025-07-29 14:46:07 -04:00