From nobody Sun Feb 8 21:27:26 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EDCBA267AF0; Fri, 2 May 2025 16:50:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746204610; cv=none; b=g4bZbB2W9VoRPgnKEaDrjBzZRC7Ggb54qCa0VoUH2GMkC5MHmnCP54nRfQDIf9FPZ36jLcdBiqSS2DaS+62BX+1G9lpzmP0aFpWrjXPyq3PSgvAWdEIsKlOi3IQ0e9XzmM7ssM4Ad8gUtSXWsXVU4TQZHIQ0fAuoaIcDXdPhOMg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746204610; c=relaxed/simple; bh=Jph6NmqNgTqJBFSZ+GDtcC6ViuoUMw6YWCVmR1fFyvE=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=S+9jQ++kKYyOxsqttTIX8bPyGbelrH5/NLc3XyQ7wLvoXKlmUH8Vvxfs3pywzx0Hl4D4yXX4cStludssurZ7Fkh2h6apR1SF32m1AEd31p2ei9oOU1jMVin9/AIm/B0TJUNSk4wP2AfokcG0v13KNCD/v2GnnvvlPmwqqEDrcU4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81D1BC4CEE4; Fri, 2 May 2025 16:50:09 +0000 (UTC) Received: from rostedt by gandalf with local (Exim 4.98.2) (envelope-from ) id 1uAtaS-0000000033C-3ha8; Fri, 02 May 2025 12:50:08 -0400 Message-ID: <20250502165008.734340489@goodmis.org> User-Agent: quilt/0.68 Date: Fri, 02 May 2025 12:47:54 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mathieu Desnoyers , Josh Poimboeuf , Peter Zijlstra , x86@kernel.org, Jiri Olsa , Namhyung Kim Subject: [PATCH v7 08/17] unwind_user/deferred: Add unwind cache References: <20250502164746.178864972@goodmis.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Josh Poimboeuf Cache the results of the unwind to ensure the unwind is only performed once, even when called by multiple tracers. The cache nr_entries gets cleared every time the task exits the kernel. When a stacktrace is requested, nr_entries gets set to the number of entries in the stacktrace. If another stacktrace is requested, if nr_entries is not zero, then it contains the same stacktrace that would be retrieved so it is not processed again and the entries is given to the caller. Co-developed-by: Steven Rostedt (Google) Signed-off-by: Josh Poimboeuf Signed-off-by: Steven Rostedt (Google) --- include/linux/entry-common.h | 2 ++ include/linux/unwind_deferred.h | 7 +++++++ include/linux/unwind_deferred_types.h | 7 ++++++- kernel/unwind/deferred.c | 27 ++++++++++++++++++++------- 4 files changed, 35 insertions(+), 8 deletions(-) diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index f94f3fdf15fc..6e850c9d3f0c 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -12,6 +12,7 @@ #include #include #include +#include =20 #include #include @@ -362,6 +363,7 @@ static __always_inline void exit_to_user_mode(void) lockdep_hardirqs_on_prepare(); instrumentation_end(); =20 + unwind_exit_to_user_mode(); user_enter_irqoff(); arch_exit_to_user_mode(); lockdep_hardirqs_on(CALLER_ADDR0); diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferre= d.h index 5064ebe38c4f..c2d760e5e257 100644 --- a/include/linux/unwind_deferred.h +++ b/include/linux/unwind_deferred.h @@ -12,6 +12,11 @@ void unwind_task_free(struct task_struct *task); =20 int unwind_deferred_trace(struct unwind_stacktrace *trace); =20 +static __always_inline void unwind_exit_to_user_mode(void) +{ + current->unwind_info.cache.nr_entries =3D 0; +} + #else /* !CONFIG_UNWIND_USER */ =20 static inline void unwind_task_init(struct task_struct *task) {} @@ -19,6 +24,8 @@ static inline void unwind_task_free(struct task_struct *t= ask) {} =20 static inline int unwind_deferred_trace(struct unwind_stacktrace *trace) {= return -ENOSYS; } =20 +static inline void unwind_exit_to_user_mode(void) {} + #endif /* !CONFIG_UNWIND_USER */ =20 #endif /* _LINUX_UNWIND_USER_DEFERRED_H */ diff --git a/include/linux/unwind_deferred_types.h b/include/linux/unwind_d= eferred_types.h index aa32db574e43..b3b7389ee6eb 100644 --- a/include/linux/unwind_deferred_types.h +++ b/include/linux/unwind_deferred_types.h @@ -2,8 +2,13 @@ #ifndef _LINUX_UNWIND_USER_DEFERRED_TYPES_H #define _LINUX_UNWIND_USER_DEFERRED_TYPES_H =20 -struct unwind_task_info { +struct unwind_cache { unsigned long *entries; + unsigned int nr_entries; +}; + +struct unwind_task_info { + struct unwind_cache cache; }; =20 #endif /* _LINUX_UNWIND_USER_DEFERRED_TYPES_H */ diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c index 5a3789e38c00..89ed04b1c527 100644 --- a/kernel/unwind/deferred.c +++ b/kernel/unwind/deferred.c @@ -12,6 +12,7 @@ int unwind_deferred_trace(struct unwind_stacktrace *trace) { struct unwind_task_info *info =3D ¤t->unwind_info; + struct unwind_cache *cache =3D &info->cache; =20 /* Should always be called from faultable context */ might_fault(); @@ -19,17 +20,29 @@ int unwind_deferred_trace(struct unwind_stacktrace *tra= ce) if (current->flags & PF_EXITING) return -EINVAL; =20 - if (!info->entries) { - info->entries =3D kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(= long), - GFP_KERNEL); - if (!info->entries) - return -ENOMEM; + if (!cache->entries) { + cache->entries =3D kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(long), + GFP_KERNEL); + if (!cache->entries) + return -ENOMEM; + } + + trace->entries =3D cache->entries; + + if (cache->nr_entries) { + /* + * The user stack has already been previously unwound in th= is + * entry context. Skip the unwind and use the cache. + */ + trace->nr =3D cache->nr_entries; + return 0; } =20 trace->nr =3D 0; - trace->entries =3D info->entries; unwind_user(trace, UNWIND_MAX_ENTRIES); =20 + cache->nr_entries =3D trace->nr; + return 0; } =20 @@ -44,5 +57,5 @@ void unwind_task_free(struct task_struct *task) { struct unwind_task_info *info =3D &task->unwind_info; =20 - kfree(info->entries); + kfree(info->cache.entries); } --=20 2.47.2