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[24.9.77.57]) by smtp.googlemail.com with ESMTPSA id w13sm10583057ilg.48.2021.03.16.23.54.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Mar 2021 23:54:33 -0700 (PDT) From: Jim Cromie To: jbaron@akamai.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org Cc: Jim Cromie Subject: [RFC PATCH v4 14/19] dyndbg: add ddebug_site(_get|_put) abstraction Date: Wed, 17 Mar 2021 00:54:07 -0600 Message-Id: <20210317065412.2890414-15-jim.cromie@gmail.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20210317065412.2890414-1-jim.cromie@gmail.com> References: <20210317065412.2890414-1-jim.cromie@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 be2e97ae2da9..1f59407b6a83 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