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66ee620f06
An upcoming change to the encoding of internal entries will set the bottom two bits to 0b10. Unfortunately, m68k only aligns some data structures to 2 bytes, so the IDR will interpret them as internal entries and things will go badly wrong. Change the radix tree so that it stops either when the node indicates that it's the bottom of the tree (shift == 0) or when the entry is not an internal entry. This means we cannot insert an arbitrary kernel pointer as a multiorder entry, but the IDR does not permit multiorder entries. Annoyingly, this means the IDR can no longer take advantage of the radix tree's ability to store a single entry at offset 0 without allocating memory. A pointer which is 2-byte aligned cannot be stored directly in the root as it would be indistinguishable from a node, so we must allocate a node in order to store a 2-byte pointer at index 0. The idr_replace() function does not take a GFP flags argument, so cannot allocate memory. If a user inserts a 4-byte aligned pointer at index 0 and then replaces it with a 2-byte aligned pointer, we must be able to store it. Arbitrary pointer values are still not permitted; pointers of the form 2 + (i * 4) for values of i between 0 and 1023 are reserved for the implementation. These are not valid kernel pointers as they would point into the zero page. This change does cause a runtime memory consumption regression for the IDA. I will recover that later. Signed-off-by: Matthew Wilcox <willy@infradead.org> Tested-by: Guenter Roeck <linux@roeck-us.net> |
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