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authorJim Cromie <jim.cromie@gmail.com>2020-07-19 17:10:58 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-07-24 17:00:10 +0200
commit4c0d77828d4f17ecae3e662728b997c0f0276204 (patch)
treefabc0dc14bf4420277e86fd54254bf6d800ad34f /lib/dynamic_debug.c
parent5aa9ffbbaeb3aba22a5d2b6a6eead1f0bcd38254 (diff)
downloadlwn-4c0d77828d4f17ecae3e662728b997c0f0276204.tar.gz
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dyndbg: export ddebug_exec_queries
Export ddebug_exec_queries() for use by modules. This will allow module authors to control all their *pr_debug*s dynamically. And since ddebug_exec_queries() is what implements "echo $query >control", it gives the same per-callsite control. Virtues of this: - simplicity. just an export. - full control over any/all subsets of callsites. - same "query/command-string" in code and console - full callsite selectivity with module file line format Format in particular deserves special attention; it is where low-hanging fruit will be found. Consider: drivers/gpu/drm/amd/display/include/logger_types.h: #define DC_LOG_SURFACE(...) pr_debug("[SURFACE]:"__VA_ARGS__) #define DC_LOG_HW_LINK_TRAINING(...) pr_debug("[HW_LINK_TRAINING]:"__VA_ARGS__) .. 9 more .. Thats 11 string prefixes, used in 804 places in drivers/gpu/** Clearly this is a systematized classification of those callsites. And one I'd expect to see repeated often. Using ddebug_exec_queries(), authors can select on those prefixes as a unitary set, equivalent to: echo "module=MODULE_NAME format=^[SURFACE]: +p" >control Trivially, those sets can be subsected with the other query terms too, say file=foo, should the author see fit. Perhaps as important, users can modify the set of enabled callsites, presumably to aid debugging by enabling helpful debug callsites, and disabling those that just clutter the info. Authors could even alter [fmlt] flags, though I dont see a good reason why they would. Perhaps harnessed by bug-logging automation to get fuller, or more minimal bug-reports. DRM drm has both drm.debug, which defines 32 categories of drm_printk logging, and entirely separate uses of pr_debug, which are dynamic on this i915 laptop, running mainline. So I can observe and report on both. The i915 driver has 118 dyndbg callsites, with following "classifications" defined in drivers/gpu/drm/i915/gvt/** $ grep 915 /proc/dynamic_debug/control | cut -d= -f2 | cut -d: -f1,2 | sort -u _ "gvt: cmd _ "gvt: core _ "gvt: dpy _ "gvt: el _ "gvt: irq _ "gvt: mm _ "gvt: mmio _ "gvt: render _ "gvt: sched _ "%s for root hub!\012" _ "Vendor defined info completion code %u\012" This classification is entirely out-of-band for control by drm.debug, and is only available to root user at the console. But module authors can activate them with ddebug_exec_queries(sprintf("format=^%s +p")), and then decide how to expose the groups to the user for max utility. drm.debug drm.debug has 32 bit-flags, and matching enum drm_debug_category values to classify the ~2943 DRM_DEBUG*() callsites in drivers/gpu The drm.debug callback could invoke ddebug_exec_queries() with 32 different hardcoded query strings, needing only (bit) ? " +p" : " -p" added. I briefly enabled drm.debug=0xff on my i915 laptop, which yielded these unique prefixes: (dmesg | cut -c17- | cut -d\] -f1 | sort -u) [drm:drm_atomic_check_only [drm [drm:drm_atomic_get_crtc_state [drm [drm:drm_atomic_get_plane_state [drm [drm:drm_atomic_nonblocking_commit [drm [drm:drm_atomic_set_fb_for_plane [drm [drm:drm_atomic_state_default_clear [drm [drm:__drm_atomic_state_free [drm [drm:drm_atomic_state_init [drm [drm:drm_crtc_vblank_helper_get_vblank_timestamp_internal [drm [drm:drm_handle_vblank [drm [drm:drm_ioctl [drm [drm:drm_mode_addfb2 [drm [drm:drm_mode_object_get [drm [drm:drm_mode_object_put.part.0 [drm [drm:drm_update_vblank_count [drm [drm:drm_vblank_enable [drm [drm:drm_vblank_restore [drm [drm:vblank_disable_fn [drm i915 0000:00:02.0: [drm:gen9_set_dc_state [i915 i915 0000:00:02.0: [drm:intel_atomic_get_global_obj_state [i915 i915 0000:00:02.0: [drm:__intel_display_power_get_domain.part.0 [i915 i915 0000:00:02.0: [drm:__intel_display_power_put_domain [i915 i915 0000:00:02.0: [drm:intel_plane_atomic_calc_changes [i915 i915 0000:00:02.0: [drm:skl_enable_dc6 [i915 Several good format=^prefixes are apparent there, and some misses. ^[drm:drm_atomic_ # misses: [drm:__drm_atomic_state_free [drm ^[drm:drm_ioctl ^[drm:drm_mode ^[drm:drm_vblank_ # misses: [drm:drm_update_vblank_count & [drm:vblank_disable_fn Its not a perfect 1:1 single format-match per class, but the misses above can be covered with 1 & 2 additional queries, which can be concatenated together with ";" separators and submitted with 1 call. Benefits: For drm, adapting DRM_DEBUG to use dynamic-debug inside could replicate (and thereby obsolete) lots of bit-checking in current DRM_DEBUG callsites, at least with JUMP_LABEL optimized code. ddebug_exec_queries() and a handful of fixed query-strings can select and thereby control the already classified callsites. With the classes mapped to queries, the enum type and parameter can be eliminated (folded away with macro magic), at least for DYNAMIC_DEBUG & JUMP_LABEL builds. Is it safe ? ddebug_exec_queries() is currently exposed to user space in several limited ways; 1 it is called from module-load callback, where it implements the $modname.dyndbg=+p "fake" parameter provided to all modules. 2 it handles query input via >control directly IOW, it is "fully" exposed to local root user; exposing the same functionality to other kernel modules is no additional risk. The other standard issue to check is locking: dyndbg has a single mutex, taken by ddebug_change to handle >control, and by ddebug_proc_(start|stop) to span `cat control`. Queries submitted via export will typically have module specified, which dramatically cuts the scan by ddebug_change vs "module=* +p". ISTM this proposed export presents no locking problems. TLDR; It would be interesting to see how drm.dyndbg=$QUERY and drm.debug=$HEXY would interact; it might be order dependent, as if given as modprobe args or in /etc/modprobe.d/ Acked-by: <jbaron@akamai.com> Signed-off-by: Jim Cromie <jim.cromie@gmail.com> Link: https://lore.kernel.org/r/20200719231058.1586423-19-jim.cromie@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'lib/dynamic_debug.c')
-rw-r--r--lib/dynamic_debug.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index e87b630bd793..1d012e597cc3 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -525,7 +525,7 @@ static int ddebug_exec_query(char *query_string, const char *modname)
last error or number of matching callsites. Module name is either
in param (for boot arg) or perhaps in query string.
*/
-static int ddebug_exec_queries(char *query, const char *modname)
+int ddebug_exec_queries(char *query, const char *modname)
{
char *split;
int i, errs = 0, exitcode = 0, rc, nfound = 0;
@@ -557,6 +557,7 @@ static int ddebug_exec_queries(char *query, const char *modname)
return exitcode;
return nfound;
}
+EXPORT_SYMBOL_GPL(ddebug_exec_queries);
#define PREFIX_SIZE 64