From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: [PATCH v2 5/8] dma-debug: Make leak-like behaviour apparent Date: Wed, 5 Dec 2018 19:56:54 +0000 Message-ID: <67d2b20b8e2ec069ffbc2f71408ce917a759d45a.1544037783.git.robin.murphy@arm.com> References: Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: hch@lst.de Cc: m.szyprowski@samsung.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, cai@gmx.us, salil.mehta@huawei.com, john.garry@huawei.com List-Id: iommu@lists.linux-foundation.org Now that we can dynamically allocate DMA debug entries to cope with drivers maintaining excessively large numbers of live mappings, a driver which *does* actually have a bug leaking mappings (and is not unloaded) will no longer trigger the "DMA-API: debugging out of memory - disabling" message until it gets to actual kernel OOM conditions, which means it could go unnoticed for a while. To that end, let's inform the user each time the pool has grown to a multiple of its initial size, which should make it apparent that they either have a leak or might want to increase the preallocation size. Signed-off-by: Robin Murphy --- v2: Move the suggestion of a leak from the message to the documentation Documentation/DMA-API.txt | 6 +++++- kernel/dma/debug.c | 13 +++++++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index 0fcb7561af1e..7a7d8a415ce8 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -747,7 +747,11 @@ driver afterwards. This filter can be disabled or changed later using debugfs. When the code disables itself at runtime this is most likely because it ran out of dma_debug_entries and was unable to allocate more on-demand. 65536 entries are preallocated at boot - if this is too low for you boot with -'dma_debug_entries=' to overwrite the default. +'dma_debug_entries=' to overwrite the default. The +code will print to the kernel log each time it has dynamically allocated +as many entries as were initially preallocated. This is to indicate that a +larger preallocation size may be appropriate, or if it happens continually +that a driver may be leaking mappings. :: diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index b1fe8b78acc4..cd9a12bf6a3a 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -693,6 +693,18 @@ static struct dma_debug_entry *__dma_entry_alloc(void) return entry; } +void __dma_entry_alloc_check_leak(void) +{ + u32 tmp = nr_total_entries % nr_prealloc_entries; + + /* Shout each time we tick over some multiple of the initial pool */ + if (tmp < DMA_DEBUG_DYNAMIC_ENTRIES) { + pr_info("dma_debug_entry pool grown to %u (%u00%%)\n", + nr_total_entries, + (nr_total_entries / nr_prealloc_entries)); + } +} + /* struct dma_entry allocator * * The next two functions implement the allocator for @@ -711,6 +723,7 @@ static struct dma_debug_entry *dma_entry_alloc(void) pr_err("debugging out of memory - disabling\n"); return NULL; } + __dma_entry_alloc_check_leak(); } entry = __dma_entry_alloc(); -- 2.19.1.dirty