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ANDROID: tracing: Make automounting in debugfs optional

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This patch creates a config that can be used to disable the automount of
tracefs in the debugfs filesystem. Since the automount happens everytime
the path /sys/kernel/debug/tracing is accessed, unmounting from
userspace is ineffective against it.
The config is intended to prevent new tracefs clients from depending on
the automounted tracefs instance mounted at /sys/kernel/debug/tracing
instead of the one at /sys/kernel/tracing. Since Android R launching
devices and newer cannot mount debugfs in production builds, the
config is intended to minimize the difference between user and
userdebug builds w.r.t to tracefs and prevent regresssions.

Bug: 184381659
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Change-Id: Ifda6df88081c8ecf23fcaf97790abc97525bca54
This commit is contained in:
Hridya Valsaraju
2021-03-30 12:55:01 -07:00
committed by Greg Kroah-Hartman
parent eacad94c98
commit 412bd71850
5 changed files with 16 additions and 0 deletions
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3
Documentation/trace/ftrace.rst
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@@ -76,6 +76,9 @@ it::
All files located in the tracefs file system will be located in that All files located in the tracefs file system will be located in that
debugfs file system directory as well. debugfs file system directory as well.
In order to not automount tracefs in the debugfs filesystem, enable the
defconfig option CONFIG_TRACEFS_DISABLE_AUTOMOUNT.
.. attention:: .. attention::
Any selected ftrace option will also create the tracefs file system. Any selected ftrace option will also create the tracefs file system.

1
arch/arm64/configs/gki_defconfig
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@@ -648,6 +648,7 @@ CONFIG_SCHEDSTATS=y
# CONFIG_DEBUG_PREEMPT is not set # CONFIG_DEBUG_PREEMPT is not set
CONFIG_BUG_ON_DATA_CORRUPTION=y CONFIG_BUG_ON_DATA_CORRUPTION=y
CONFIG_TRACE_MMIO_ACCESS=y CONFIG_TRACE_MMIO_ACCESS=y
CONFIG_TRACEFS_DISABLE_AUTOMOUNT=y
CONFIG_KUNIT=y CONFIG_KUNIT=y
CONFIG_KUNIT_DEBUGFS=y CONFIG_KUNIT_DEBUGFS=y
# CONFIG_RUNTIME_TESTING_MENU is not set # CONFIG_RUNTIME_TESTING_MENU is not set

1
arch/x86/configs/gki_defconfig
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@@ -586,6 +586,7 @@ CONFIG_DETECT_HUNG_TASK=y
CONFIG_WQ_WATCHDOG=y CONFIG_WQ_WATCHDOG=y
CONFIG_SCHEDSTATS=y CONFIG_SCHEDSTATS=y
CONFIG_BUG_ON_DATA_CORRUPTION=y CONFIG_BUG_ON_DATA_CORRUPTION=y
CONFIG_TRACEFS_DISABLE_AUTOMOUNT=y
CONFIG_UNWINDER_FRAME_POINTER=y CONFIG_UNWINDER_FRAME_POINTER=y
CONFIG_KUNIT=y CONFIG_KUNIT=y
CONFIG_KUNIT_DEBUGFS=y CONFIG_KUNIT_DEBUGFS=y

5
kernel/trace/Kconfig
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@@ -103,6 +103,11 @@ config PREEMPTIRQ_TRACEPOINTS
Create preempt/irq toggle tracepoints if needed, so that other parts Create preempt/irq toggle tracepoints if needed, so that other parts
of the kernel can use them to generate or add hooks to them. of the kernel can use them to generate or add hooks to them.
menuconfig TRACEFS_DISABLE_AUTOMOUNT
bool "Do not autmount tracefs in the debugfs filesystem"
help
Provides an option to not automount tracefs in /sys/kernel/debug/tracing.
# All tracer options should select GENERIC_TRACER. For those options that are # All tracer options should select GENERIC_TRACER. For those options that are
# enabled by all tracers (context switch and event tracer) they select TRACING. # enabled by all tracers (context switch and event tracer) they select TRACING.
# This allows those options to appear when no other tracer is selected. But the # This allows those options to appear when no other tracer is selected. But the

6
kernel/trace/trace.c
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@@ -9010,6 +9010,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
ftrace_init_tracefs(tr, d_tracer); ftrace_init_tracefs(tr, d_tracer);
} }
#ifndef CONFIG_TRACEFS_DISABLE_AUTOMOUNT
static struct vfsmount *trace_automount(struct dentry *mntpt, void *ingore) static struct vfsmount *trace_automount(struct dentry *mntpt, void *ingore)
{ {
struct vfsmount *mnt; struct vfsmount *mnt;
@@ -9031,6 +9032,7 @@ static struct vfsmount *trace_automount(struct dentry *mntpt, void *ingore)
return mnt; return mnt;
} }
#endif
/** /**
* tracing_init_dentry - initialize top level trace array * tracing_init_dentry - initialize top level trace array
@@ -9055,6 +9057,7 @@ int tracing_init_dentry(void)
if (WARN_ON(!tracefs_initialized())) if (WARN_ON(!tracefs_initialized()))
return -ENODEV; return -ENODEV;
#ifndef CONFIG_TRACEFS_DISABLE_AUTOMOUNT
/* /*
* As there may still be users that expect the tracing * As there may still be users that expect the tracing
* files to exist in debugfs/tracing, we must automount * files to exist in debugfs/tracing, we must automount
@@ -9063,6 +9066,9 @@ int tracing_init_dentry(void)
*/ */
tr->dir = debugfs_create_automount("tracing", NULL, tr->dir = debugfs_create_automount("tracing", NULL,
trace_automount, NULL); trace_automount, NULL);
#else
tr->dir = ERR_PTR(-ENODEV);
#endif
return 0; return 0;
} }