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a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1677013910; bh=LAT6es1zlcxHgyXQ+ccAd1DGKcAvO/9IswEU0C+E8Yk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sD/1eaVnzd86RfhuQGs9V1soHDsH7AjM4ll3w5rmohEWwV3OxFGG6XcBwMOm64c7a vnPXQliyyk3o1rTE4U2EYLVD5T/2Yany8n6FKAwF6q4dBLODMzeyqKlJKd6ezroU7z lPJ2zTjDZZbJ63Li5seDtiZFeFZ3DDyOQdlWCWyw= From: Beau Belgrave To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, dcook@linux.microsoft.com, alanau@linux.microsoft.com, brauner@kernel.org, akpm@linux-foundation.org, ebiederm@xmission.com, keescook@chromium.org, tglx@linutronix.de Cc: linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v8 04/11] tracing/user_events: Fixup enable faults asyncly Date: Tue, 21 Feb 2023 13:11:36 -0800 Message-Id: <20230221211143.574-5-beaub@linux.microsoft.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230221211143.574-1-beaub@linux.microsoft.com> References: <20230221211143.574-1-beaub@linux.microsoft.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 5D03A20009 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 9ddqbik84tk7aa988p6e6xwtqk7shfb5 X-HE-Tag: 1677013911-21828 X-HE-Meta: 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 evBxxSPS niWdZ1A84vNzjIjrjwijA0IHmBiZZ+AKGXyWI/dxnUpNUX2Au0WLQAzcb1/3kX6g5ERVMxMiXBjcWHqJgDk9i70O78ULcpT5/kSaoKsmnEs13nRx/nzdNF6nPzaTeK6K89sUvaP41uG/UaDLI+1mpKC3+50zLje4gwCODlfcZhhAIXjNe9bWpxmkSzVBV9BF2MCGtNRWZE0/YsNHilSTUIJJADN7g3ONxms6F6CNyHcHjv1N3ItfAuHMyJvSN010aKoPfVXoVp48vHsOT9+W6L+2l2SS+ayL/4uz5d2szORqfqXM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: When events are enabled within the various tracing facilities, such as ftrace/perf, the event_mutex is held. As events are enabled pages are accessed. We do not want page faults to occur under this lock. Instead queue the fault to a workqueue to be handled in a process context safe way without the lock. The enable address is marked faulting while the async fault-in occurs. This ensures that we don't attempt to fault-in more than is necessary. Once the page has been faulted in, an address write is re-attempted. If the page couldn't fault-in, then we wait until the next time the event is enabled to prevent any potential infinite loops. Signed-off-by: Beau Belgrave --- kernel/trace/trace_events_user.c | 120 +++++++++++++++++++++++++++++-- 1 file changed, 114 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c index 553a82ee7aeb..86bda1660536 100644 --- a/kernel/trace/trace_events_user.c +++ b/kernel/trace/trace_events_user.c @@ -99,9 +99,23 @@ struct user_event_enabler { /* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */ #define ENABLE_VAL_BIT_MASK 0x3F +/* Bit 6 is for faulting status of enablement */ +#define ENABLE_VAL_FAULTING_BIT 6 + /* Only duplicate the bit value */ #define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK +#define ENABLE_BITOPS(e) ((unsigned long *)&(e)->values) + +/* Used for asynchronous faulting in of pages */ +struct user_event_enabler_fault { + struct work_struct work; + struct user_event_mm *mm; + struct user_event_enabler *enabler; +}; + +static struct kmem_cache *fault_cache; + /* Global list of memory descriptors using user_events */ static LIST_HEAD(user_event_mms); static DEFINE_SPINLOCK(user_event_mms_lock); @@ -263,7 +277,85 @@ static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr) } static int user_event_enabler_write(struct user_event_mm *mm, - struct user_event_enabler *enabler) + struct user_event_enabler *enabler, + bool fixup_fault); + +static void user_event_enabler_fault_fixup(struct work_struct *work) +{ + struct user_event_enabler_fault *fault = container_of( + work, struct user_event_enabler_fault, work); + struct user_event_enabler *enabler = fault->enabler; + struct user_event_mm *mm = fault->mm; + unsigned long uaddr = enabler->addr; + int ret; + + ret = user_event_mm_fault_in(mm, uaddr); + + if (ret && ret != -ENOENT) { + struct user_event *user = enabler->event; + + pr_warn("user_events: Fault for mm: 0x%pK @ 0x%llx event: %s\n", + mm->mm, (unsigned long long)uaddr, EVENT_NAME(user)); + } + + /* Prevent state changes from racing */ + mutex_lock(&event_mutex); + + /* + * If we managed to get the page, re-issue the write. We do not + * want to get into a possible infinite loop, which is why we only + * attempt again directly if the page came in. If we couldn't get + * the page here, then we will try again the next time the event is + * enabled/disabled. + */ + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + if (!ret) { + mmap_read_lock(mm->mm); + user_event_enabler_write(mm, enabler, true); + mmap_read_unlock(mm->mm); + } + + mutex_unlock(&event_mutex); + + /* In all cases we no longer need the mm or fault */ + user_event_mm_put(mm); + kmem_cache_free(fault_cache, fault); +} + +static bool user_event_enabler_queue_fault(struct user_event_mm *mm, + struct user_event_enabler *enabler) +{ + struct user_event_enabler_fault *fault; + + fault = kmem_cache_zalloc(fault_cache, GFP_NOWAIT | __GFP_NOWARN); + + if (!fault) + return false; + + INIT_WORK(&fault->work, user_event_enabler_fault_fixup); + fault->mm = user_event_mm_get(mm); + fault->enabler = enabler; + + /* Don't try to queue in again while we have a pending fault */ + set_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + if (!schedule_work(&fault->work)) { + /* Allow another attempt later */ + clear_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)); + + user_event_mm_put(mm); + kmem_cache_free(fault_cache, fault); + + return false; + } + + return true; +} + +static int user_event_enabler_write(struct user_event_mm *mm, + struct user_event_enabler *enabler, + bool fixup_fault) { unsigned long uaddr = enabler->addr; unsigned long *ptr; @@ -278,11 +370,19 @@ static int user_event_enabler_write(struct user_event_mm *mm, if (refcount_read(&mm->tasks) == 0) return -ENOENT; + if (unlikely(test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))) + return -EBUSY; + ret = pin_user_pages_remote(mm->mm, uaddr, 1, FOLL_WRITE | FOLL_NOFAULT, &page, NULL, NULL); - if (ret <= 0) { - pr_warn("user_events: Enable write failed\n"); + if (unlikely(ret <= 0)) { + if (!fixup_fault) + return -EFAULT; + + if (!user_event_enabler_queue_fault(mm, enabler)) + pr_warn("user_events: Unable to queue fault handler\n"); + return -EFAULT; } @@ -314,7 +414,7 @@ static void user_event_enabler_update(struct user_event *user) list_for_each_entry_rcu(enabler, &mm->enablers, link) if (enabler->event == user) - user_event_enabler_write(mm, enabler); + user_event_enabler_write(mm, enabler, true); rcu_read_unlock(); mmap_read_unlock(mm->mm); @@ -562,7 +662,7 @@ static struct user_event_enabler /* Attempt to reflect the current state within the process */ mmap_read_lock(user_mm->mm); - *write_result = user_event_enabler_write(user_mm, enabler); + *write_result = user_event_enabler_write(user_mm, enabler, false); mmap_read_unlock(user_mm->mm); /* @@ -2201,16 +2301,24 @@ static int __init trace_events_user_init(void) { int ret; + fault_cache = KMEM_CACHE(user_event_enabler_fault, 0); + + if (!fault_cache) + return -ENOMEM; + init_group = user_event_group_create(&init_user_ns); - if (!init_group) + if (!init_group) { + kmem_cache_destroy(fault_cache); return -ENOMEM; + } ret = create_user_tracefs(); if (ret) { pr_warn("user_events could not register with tracefs\n"); user_event_group_destroy(init_group); + kmem_cache_destroy(fault_cache); init_group = NULL; return ret; }