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This directory is >> used to collect the dmabuf stats and it is created through >> dma_buf_stats_setup(). At current, failure to create this directory >> entry can make the dma_buf_export() to fail. >> >> Now, as the get_next_ino() can definitely give a repetitive inode no >> causing the directory entry creation to fail with -EEXIST. This is a >> problem on the systems where dmabuf stats functionality is enabled on >> the production builds can make the dma_buf_export(), though the dmabuf >> memory is allocated successfully, to fail just because it couldn't >> create stats entry. > Then maybe we should not fail the creation path of the kobject fails to > be created? It's just for debugging, it should be fine if the creation > of it isn't there. Well if it's just for debugging then it should be under debugfs and not sysfs. >> This issue we are able to see on the snapdragon system within 13 days >> where there already exists a directory with inode no "122602" so >> dma_buf_stats_setup() failed with -EEXIST as it is trying to create >> the same directory entry. >> >> To make the directory entry as unique, append the inode creation time to >> the inode. With this change the stats directory entries will be in the >> format of: /sys/kernel/dmabuf/buffers/-> secs>. > As you are changing the format here, shouldn't the Documentation/ABI/ > entry for this also be changed? As far as I can see that is even an UAPI break, not sure if we can allow that. > And what's to keep the seconds field from also being the same? Well exporting two DMA-bufs with the same ino in the same nanosecond should be basically impossible, but I would rather opt for using a 64bit atomic in that function. This should be 100% UAPI compatible and even if we manage to create one buffer ever ns we need ~500years to wrap around. Regards, Christian. > > thanks, > > greg k-h