dma-debug: Make leak-like behaviour apparent

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 <robin.murphy@arm.com>
Tested-by: Qian Cai <cai@lca.pw>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 0fcb756..7a7d8a4 100644 (file)
--- 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=<your_desired_number>' to overwrite the default.
+'dma_debug_entries=<your_desired_number>' 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 ef7c90b..912c23f 100644 (file)
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -691,6 +691,18 @@ 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
@@ -710,6 +722,7 @@ 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();