Replace direct ->site refs with _get(),_put() internal API. Right
now, _get() just returns ->site and _put() does nothing. Later we can
replace that implementation with one using ->module_index to fetch
then forget site data dynamically.
Several approaches are possible:
A: !site -> fill from backing store
1st try at this is/was using zram. At init, it copied each callsite
into a zs-allocation, and all site-> refs afterward went thru
_get/_put to zs-map on demand, and zs-unmap the site info. This
worked until I tried to keep callsites mapped while they're enabled,
when it gave lockdep warns/panics. IIRC theres a zram patchset doing
something with locking; I need to retry this approach, even if other
options are better, this might be a validating use case.
B: block store
Another approach is to compress the new linker section, using some
algorithm thats good at indexed decompression. I probed this
approach, using objcopy, unsuccessfully:
objcopy --dump-section __dyndbg=dd \
--dump-section __dyndbg_sites=ddsites $IMG
>From vmlinux.o dumps were mostly empty (pre-link/reloc data?)
and vmlinux didnt have the section.
C: callsite composed from __dyndbg[N] & __dyndbg_site[N]
We know _ddebug records are in a vector, either in the builtin
__dyndbg linker section, or the same from a modprobed one. The
builtin section has all builtin module sub-sections catenated
dogether.
At init, we iterate over the section, and "parse it" by creating a
ddebug_table for each module with prdebugs. ddebug_table.num_debugs
remembers the size of each modules' vector of prdebugs.
We need a few things:
- _ddebug.index field, which knows offset to start of this sub-vector.
this new field will be "free" because the struct has padding.
it can be initialized during init, then RO.
- a back-pointer at the beginning of the sub-vector, to the
ddebug_table "owning" (but not containing) this sub-vector of
prdebugs.
If we had both, we could get from the ddebug element to its vector
root, back up to the owning ddebug_table, then down to the _callsite
vector, and index to the right element. While slower than a pointer
deref, this is a cold path, and it allows elimination of the
per-callsite pointer member, thus greater density of the sections, and
still can support sparse site info.
That back-pointer feels tricky. It needs to be 1st in the sub-vector
D: (C1?) add a header record to each sub-vector
If we can insert a header record into each modules' __dyndbg* section
sub-vectors, we can simplify the cold path above; a single sites*
pointer in the header can give us access to __dyndbg_sites[N]
Signed-off-by: Jim Cromie <jim.cro...@gmail.com>
---
lib/dynamic_debug.c | 31 +++++++++++++++++++++++++------
1 file changed, 25 insertions(+), 6 deletions(-)
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 5529b17461ae..34329e323ed5 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -144,6 +144,14 @@ static void vpr_info_dq(const struct ddebug_query *query,
const char *msg)
query->first_lineno, query->last_lineno);
}
+static struct _ddebug_site *ddebug_site_get(struct _ddebug *dp)
+{
+ return dp->site; /* passthru abstraction */
+}
+static inline void ddebug_site_put(struct _ddebug *dp)
+{
+}
+
static int ddebug_match_site(const struct ddebug_query *query,
const struct _ddebug *dp,
const struct _ddebug_site *dc)
@@ -239,16 +247,18 @@ static int ddebug_change(const struct ddebug_query *query,
for (i = 0; i < dt->num_ddebugs; i++) {
struct _ddebug *dp = &dt->ddebugs[i];
- struct _ddebug_site *dc = dp->site;
+ struct _ddebug_site *dc;
+
+ dc = ddebug_site_get(dp);
if (!ddebug_match_site(query, dp, dc))
- continue;
+ goto skipsite;
nfound++;
newflags = (dp->flags & modifiers->mask) |
modifiers->flags;
if (newflags == dp->flags)
- continue;
+ goto skipsite;
ddebug_alter_site(dp, modifiers);
@@ -264,6 +274,9 @@ static int ddebug_change(const struct ddebug_query *query,
dt->mod_name, dp->lineno,
ddebug_describe_flags(dp->flags,
&fbuf),
dp->format);
+
+ skipsite:
+ ddebug_site_put(dp);
}
}
mutex_unlock(&ddebug_lock);
@@ -633,11 +646,11 @@ static int remaining(int wrote)
return 0;
}
-static char *__dynamic_emit_prefix(const struct _ddebug *dp, char *buf)
+static char *__dynamic_emit_prefix(struct _ddebug *dp, char *buf)
{
int pos_after_tid;
int pos = 0;
- const struct _ddebug_site *desc = dp->site;
+ const struct _ddebug_site *desc;
*buf = '\0';
@@ -653,6 +666,7 @@ static char *__dynamic_emit_prefix(const struct _ddebug
*dp, char *buf)
if (!(dp->flags & _DPRINTK_FLAGS_INCL_ANYSITE))
return buf;
+ desc = ddebug_site_get(dp);
if (desc) {
if (dp->flags & _DPRINTK_FLAGS_INCL_MODNAME)
pos += snprintf(buf + pos, remaining(pos), "%s:",
@@ -670,6 +684,8 @@ static char *__dynamic_emit_prefix(const struct _ddebug
*dp, char *buf)
if (pos >= PREFIX_SIZE)
buf[PREFIX_SIZE - 1] = '\0';
+ ddebug_site_put(dp);
+
return buf;
}
@@ -952,7 +968,8 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
return 0;
}
- dc = dp->site;
+ dc = ddebug_site_get(dp);
+
if (dc) {
seq_printf(m, "%s:%u [%s]%s =%s \"",
trim_prefix(dc->filename), dp->lineno,
@@ -968,6 +985,8 @@ static int ddebug_proc_show(struct seq_file *m, void *p)
seq_puts(m, "\"\n");
}
+ ddebug_site_put(dp);
+
return 0;
}
--
2.29.2
