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Page fault tracepoints can be disabled as with ubuntu-artful (see bel… #1034

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merged 2 commits into from
Jan 12, 2018
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Page fault tracepoints can be disabled as with ubuntu-artful (see bel… #1034

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Page fault tracepoints can be disabled as with ubuntu-artful (see bel…
anoop-sysd Jan 11, 2018
b5967dd
Fix initialization of static.
anoop-sysd Jan 12, 2018
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17 changes: 13 additions & 4 deletions driver/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -196,9 +196,12 @@ static struct tracepoint *tp_sched_switch;
static struct tracepoint *tp_signal_deliver;
#endif
#ifdef CAPTURE_PAGE_FAULTS
// Even in kernels that can support page fault tracepoints, tracepoints may be
// disabled so check if g_fault_tracepoint_disabled is set.
static struct tracepoint *tp_page_fault_user;
static struct tracepoint *tp_page_fault_kernel;
static bool g_fault_tracepoint_registered;
static bool g_fault_tracepoint_disabled = false;
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Minor: initializing a static to false is not good practice according to kernel coding conventions, if you run your patch against checkpatch.pl in the kernel tree it should complain.

#endif

#ifdef _DEBUG
Expand Down Expand Up @@ -1027,6 +1030,12 @@ static long ppm_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
#ifdef CAPTURE_PAGE_FAULTS
ASSERT(g_tracepoint_registered);

if (g_fault_tracepoint_disabled) {
ret = 0;
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We need to return an error here and propagate it to the user. If not, they could run sysdig --page-faults and silently fail.

pr_info("kernel page fault tracepoints are disabled\n");
goto cleanup_ioctl;
}

if (!g_fault_tracepoint_registered) {
ret = compat_register_trace(page_fault_probe, "page_fault_user", tp_page_fault_user);
if (ret) {
Expand Down Expand Up @@ -2199,12 +2208,12 @@ static int get_tracepoint_handles(void)
#endif
#ifdef CAPTURE_PAGE_FAULTS
if (!tp_page_fault_user) {
pr_err("failed to find page_fault_user tracepoint\n");
return -ENOENT;
pr_notice("failed to find page_fault_user tracepoint, disabling page-faults\n");
g_fault_tracepoint_disabled = true;
}
if (!tp_page_fault_kernel) {
pr_err("failed to find page_fault_kernel tracepoint\n");
return -ENOENT;
pr_notice("failed to find page_fault_kernel tracepoint, disabling page-faults\n");
g_fault_tracepoint_disabled = true;
}
#endif

Expand Down