From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1521561785; cv=none; d=google.com; s=arc-20160816; b=HbSOM3BmX27zkMlHnBG5ksijbcmOLV9Ad2tTzZ4LoCAstpRsMuw6sW/WaRnf0ADAGv ETdShk2bPEWLJSPsb3c4hbMV/ldToQcYNRJFiEnWhO1BQp2AxML27spcIeY6dbUe25Qm k3IYqMyHwX6jU9wiW3rrIzJBmk10mVOWeoDZ6SI/lyN9X9lM/SzWIxjUOpog7gdj7CIq 5KDjuIUnOfN8gWritCimOuhUs+XvWpQgBROfZwH2cyoXvYv1UPHj8cwlI49ohX01v8x1 xHSYWWs4qYxEERJS/bYkPJkawQMbNpMltDxtFnzPmtdrwQ/ztXmATgsF8/YXlpMLralU VklA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=message-id:date:subject:cc:to:from:dkim-signature :arc-authentication-results; bh=GFmYyDaRXNdyDXS+ka8h/XRlijrUjUYsYDQzfsLVzYo=; b=cj1j7joOE0ux2N9HeZefydR2Mbs7f+1m4f6NP2JpEP9p9AyT/bVlmbui6O7NKz9gQr ApkhVG51Trs6B5zEJLn17gPo7aDF/6JQKrPh76FpT6PHImI0v6O6KYmv35Eqn3UO4kvo UT49ULZR4wTjWW01wRmhK8LnYYugZJspKTW6WEpp7PxJP+rl9z7rsXtQb3X3a82VWCp4 TptNvqK/NMFTxG4DJY2UMHVnONnfN2d5XyNrZLObqliYxGiiBtcAKqtI5KmIeRgnQ+dy PkvPEYzmiJcvf3CODU1LhoJOLZADeFaNtQ06pLLjWHrksAeZ5uHEbAhevw1Rvv1jHP3p pl7A== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@ffwll.ch header.s=google header.b=VK93NXqh; spf=neutral (google.com: 209.85.220.65 is neither permitted nor denied by best guess record for domain of daniel.vetter@ffwll.ch) smtp.mailfrom=daniel.vetter@ffwll.ch Authentication-Results: mx.google.com; dkim=pass header.i=@ffwll.ch header.s=google header.b=VK93NXqh; spf=neutral (google.com: 209.85.220.65 is neither permitted nor denied by best guess record for domain of daniel.vetter@ffwll.ch) smtp.mailfrom=daniel.vetter@ffwll.ch X-Google-Smtp-Source: AG47ELtp+I1gSmRsjKXTaqDUpqpbByVDJzQVFra2BQsHDdtP1UEetTI9ngzaXowNaBYHp49AEl5tbg== From: Daniel Vetter To: Intel Graphics Development Cc: LKML , Daniel Vetter , Philippe Ombredanne , Greg Kroah-Hartman , Thomas Gleixner , Kate Stewart , Waiman Long , Daniel Vetter Subject: [PATCH] RFC: debugobjects: capture stack traces at _init() time Date: Tue, 20 Mar 2018 17:02:58 +0100 Message-Id: <20180320160258.11381-1-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.16.2 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595473170470511522?= X-GMAIL-MSGID: =?utf-8?q?1595473170470511522?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Sometimes it's really easy to know which object has gone boom and where the offending code is, and sometimes it's really hard. One case we're trying to hunt down is when module unload catches a live debug object, with a module with lots of them. Capture a full stack trace from debug_object_init() and dump it when there's a problem. FIXME: Should we have a separate Kconfig knob for the backtraces, they're quite expensive? Atm I'm just selecting it for the general debug object stuff. v2: Drop the locks for gathering&storing the backtrace. This is required because depot_save_stack can call free_pages (to drop it's preallocation), which can call debug_check_no_obj_freed, which will recurse into the db->lock spinlocks. Cc: Philippe Ombredanne Cc: Greg Kroah-Hartman Cc: Thomas Gleixner Cc: Kate Stewart Cc: Daniel Vetter Cc: Waiman Long Signed-off-by: Daniel Vetter --- include/linux/debugobjects.h | 2 ++ lib/Kconfig.debug | 1 + lib/debugobjects.c | 57 +++++++++++++++++++++++++++++++++++++++----- 3 files changed, 54 insertions(+), 6 deletions(-) diff --git a/include/linux/debugobjects.h b/include/linux/debugobjects.h index afc416e5dcab..d3a6ca1a7756 100644 --- a/include/linux/debugobjects.h +++ b/include/linux/debugobjects.h @@ -4,6 +4,7 @@ #include #include +#include enum debug_obj_state { ODEBUG_STATE_NONE, @@ -31,6 +32,7 @@ struct debug_obj { unsigned int astate; void *object; struct debug_obj_descr *descr; + depot_stack_handle_t stack; }; /** diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 64155e310a9f..894dd792e771 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -442,6 +442,7 @@ source mm/Kconfig.debug config DEBUG_OBJECTS bool "Debug object operations" depends on DEBUG_KERNEL + select STACKDEPOT help If you say Y here, additional code will be inserted into the kernel to track the life time of various objects and validate diff --git a/lib/debugobjects.c b/lib/debugobjects.c index 2f5349c6e81a..2acad7150bee 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -19,6 +19,7 @@ #include #include #include +#include #define ODEBUG_HASH_BITS 14 #define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS) @@ -30,6 +31,8 @@ #define ODEBUG_CHUNK_SIZE (1 << ODEBUG_CHUNK_SHIFT) #define ODEBUG_CHUNK_MASK (~(ODEBUG_CHUNK_SIZE - 1)) +#define ODEBUG_STACKDEPTH 32 + struct debug_bucket { struct hlist_head list; raw_spinlock_t lock; @@ -280,15 +283,24 @@ static void debug_print_object(struct debug_obj *obj, char *msg) { struct debug_obj_descr *descr = obj->descr; static int limit; + unsigned long entries[ODEBUG_STACKDEPTH]; + struct stack_trace trace = { + .entries = entries, + .max_entries = ODEBUG_STACKDEPTH + }; + if (limit < 5 && descr != descr_test) { void *hint = descr->debug_hint ? descr->debug_hint(obj->object) : NULL; limit++; + depot_fetch_stack(obj->stack, &trace); WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) " "object type: %s hint: %pS\n", msg, obj_states[obj->state], obj->astate, descr->name, hint); + pr_err("ODEBUG: debug object originally initialized at:\n"); + print_stack_trace(&trace, 2); } debug_objects_warnings++; } @@ -328,6 +340,24 @@ static void debug_object_is_on_stack(void *addr, int onstack) WARN_ON(1); } +static noinline depot_stack_handle_t save_stack(struct debug_obj *obj) +{ + unsigned long entries[ODEBUG_STACKDEPTH]; + struct stack_trace trace = { + .entries = entries, + .max_entries = ODEBUG_STACKDEPTH, + .skip = 2 + }; + + save_stack_trace(&trace); + if (trace.nr_entries != 0 && + trace.entries[trace.nr_entries-1] == ULONG_MAX) + trace.nr_entries--; + + /* May be called under spinlock, so avoid sleeping */ + return depot_save_stack(&trace, GFP_NOWAIT); +} + static void __debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack) { @@ -344,14 +374,29 @@ __debug_object_init(void *addr, struct debug_obj_descr *descr, int onstack) obj = lookup_object(addr, db); if (!obj) { - obj = alloc_object(addr, db, descr); + depot_stack_handle_t stack; + + /* + * must drop locks while storing the stack trace to avoid + * recursive deadlock through depot_save_stack + * allocating/freeing memory. + */ + raw_spin_unlock_irqrestore(&db->lock, flags); + stack = save_stack(obj); + raw_spin_lock_irqsave(&db->lock, flags); + + obj = lookup_object(addr, db); if (!obj) { - debug_objects_enabled = 0; - raw_spin_unlock_irqrestore(&db->lock, flags); - debug_objects_oom(); - return; + obj = alloc_object(addr, db, descr); + if (!obj) { + debug_objects_enabled = 0; + raw_spin_unlock_irqrestore(&db->lock, flags); + debug_objects_oom(); + return; + } + debug_object_is_on_stack(addr, onstack); + obj->stack = stack; } - debug_object_is_on_stack(addr, onstack); } switch (obj->state) { -- 2.16.2