fs_fat32: Do not dirty the the buffer on non changes#175
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davids5 wants to merge 1 commit intopx4_firmware_nuttx-10.1.0+from
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fs_fat32: Do not dirty the the buffer on non changes#175davids5 wants to merge 1 commit intopx4_firmware_nuttx-10.1.0+from
davids5 wants to merge 1 commit intopx4_firmware_nuttx-10.1.0+from
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davids5
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For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen #175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
davids5
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For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen PX4/NuttX#175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
xiaoxiang781216
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Dec 23, 2021
For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen PX4/NuttX#175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
dagar
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Dec 23, 2021
…write For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen #175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
dagar
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that referenced
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Dec 23, 2021
…write For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen #175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
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This is solved at the point of control for all things using FS. |
Gary-Hobson
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Jan 18, 2022
For FAT the same buffer is used for read and writes, there is a possibility a cache line is dirty. But the fs is not dirty and will not write the sector to disk. This can be seen PX4/NuttX#175 When the system is busy that cache line can be evicted after the RX DMA has completed and overwrite the data in memory. The solution is to invalidate before the DMA to prevent an evection causing an overwite, and after the DMA it to insure coherency.
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Summary
This the root cause of the seek error. The d-cache is dirty-ed by the in-place Directory information update into
fs_buffer. However if the the directory information is the same it will not be written out. This leaves the dirty cache lines in the buffer. On the next read of the FAT Sector, if eviction happens the dirty lines will overwrite the data in the DMA buffer.Impact
seek fails on the FAT FS. because the in memory copy of the FAT is corrupted.
Testing
16 threads of
tests datamanon PX4