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SubjectRe: [PATCH v2] ftrace: fix recursive locking direct_mutex in ftrace_modify_direct_caller

Minor nit, just change the subject to start with a capital letter.

ftrace: Fix recursive locking direct_mutex in ftrace_modify_direct_caller

Other than that, this looks good.

Do you want to put this through your tree, or do you want me to take it?

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve


On Mon, 26 Sep 2022 17:41:46 -0700
Song Liu <song@kernel.org> wrote:

> Naveen reported recursive locking of direct_mutex with sample
> ftrace-direct-modify.ko:
>
> [ 74.762406] WARNING: possible recursive locking detected
> [ 74.762887] 6.0.0-rc6+ #33 Not tainted
> [ 74.763216] --------------------------------------------
> [ 74.763672] event-sample-fn/1084 is trying to acquire lock:
> [ 74.764152] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
> register_ftrace_function+0x1f/0x180
> [ 74.764922]
> [ 74.764922] but task is already holding lock:
> [ 74.765421] ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
> modify_ftrace_direct+0x34/0x1f0
> [ 74.766142]
> [ 74.766142] other info that might help us debug this:
> [ 74.766701] Possible unsafe locking scenario:
> [ 74.766701]
> [ 74.767216] CPU0
> [ 74.767437] ----
> [ 74.767656] lock(direct_mutex);
> [ 74.767952] lock(direct_mutex);
> [ 74.768245]
> [ 74.768245] *** DEADLOCK ***
> [ 74.768245]
> [ 74.768750] May be due to missing lock nesting notation
> [ 74.768750]
> [ 74.769332] 1 lock held by event-sample-fn/1084:
> [ 74.769731] #0: ffffffff86c9d6b0 (direct_mutex){+.+.}-{3:3}, at: \
> modify_ftrace_direct+0x34/0x1f0
> [ 74.770496]
> [ 74.770496] stack backtrace:
> [ 74.770884] CPU: 4 PID: 1084 Comm: event-sample-fn Not tainted ...
> [ 74.771498] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ...
> [ 74.772474] Call Trace:
> [ 74.772696] <TASK>
> [ 74.772896] dump_stack_lvl+0x44/0x5b
> [ 74.773223] __lock_acquire.cold.74+0xac/0x2b7
> [ 74.773616] lock_acquire+0xd2/0x310
> [ 74.773936] ? register_ftrace_function+0x1f/0x180
> [ 74.774357] ? lock_is_held_type+0xd8/0x130
> [ 74.774744] ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [ 74.775213] __mutex_lock+0x99/0x1010
> [ 74.775536] ? register_ftrace_function+0x1f/0x180
> [ 74.775954] ? slab_free_freelist_hook.isra.43+0x115/0x160
> [ 74.776424] ? ftrace_set_hash+0x195/0x220
> [ 74.776779] ? register_ftrace_function+0x1f/0x180
> [ 74.777194] ? kfree+0x3e1/0x440
> [ 74.777482] ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [ 74.777941] ? __schedule+0xb40/0xb40
> [ 74.778258] ? register_ftrace_function+0x1f/0x180
> [ 74.778672] ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [ 74.779128] register_ftrace_function+0x1f/0x180
> [ 74.779527] ? ftrace_set_filter_ip+0x33/0x70
> [ 74.779910] ? __schedule+0xb40/0xb40
> [ 74.780231] ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [ 74.780678] ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [ 74.781147] ftrace_modify_direct_caller+0x5b/0x90
> [ 74.781563] ? 0xffffffffa0201000
> [ 74.781859] ? my_tramp1+0xf/0xf [ftrace_direct_modify]
> [ 74.782309] modify_ftrace_direct+0x1b2/0x1f0
> [ 74.782690] ? __schedule+0xb40/0xb40
> [ 74.783014] ? simple_thread+0x2a/0xb0 [ftrace_direct_modify]
> [ 74.783508] ? __schedule+0xb40/0xb40
> [ 74.783832] ? my_tramp2+0x11/0x11 [ftrace_direct_modify]
> [ 74.784294] simple_thread+0x76/0xb0 [ftrace_direct_modify]
> [ 74.784766] kthread+0xf5/0x120
> [ 74.785052] ? kthread_complete_and_exit+0x20/0x20
> [ 74.785464] ret_from_fork+0x22/0x30
> [ 74.785781] </TASK>
>
> Fix this by using register_ftrace_function_nolock in
> ftrace_modify_direct_caller.
>
> Fixes: 53cd885bc5c3 ("ftrace: Allow IPMODIFY and DIRECT ops on the same function")
> Reported-and-tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> Signed-off-by: Song Liu <song@kernel.org>
>

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