> Alan Cox <[EMAIL PROTECTED]> writes: > > The preferable one for performance is certainly to backport the > > 2.4 changes This patch against stock 2.2.19 is a backport of the task structure ptrace flag of Linux 2.4. It is available at http://www.cs.wisc.edu/~zandy/ptrace As we reported a couple weeks ago, under Linux 2.2 ptrace can globally corrupt the FPU on SMPs. Linus identified the problem as a race between ptrace and the FPU trap handler over the process flags. The ptrace flag introduced in 2.4 eliminates the race. This port is faithful to the 2.4 design. Essentially it: - Adds a new variable `ptrace' to the task structure; - Adds new constants for this variable (PT_PTRACED etc.) and removes the corresponding old ones (PF_PTRACED etc.); - Replaces every ptrace-context reference to `flags' with a reference to `ptrace', and updates the constants used accordingly; - Updates ptrace offset constants, loads, and comparisons in assembly files. The patch is complete for all platforms except ARM. On ARM, I didn't understand the meaning of the offset constants used in the assembly, so I didn't try to fix them. The patch does include the necessary changes to C files on ARM. We have applied (cleanly), compiled (cleanly) and tested the patch on an x86 SMP, one of the same ones on which we saw FPU corruption. We have verified that FPU corruption cannot be produced, and that gdb and strace still function. We have not tested any other platform. Please direct any questions or problems with the patch to Victor Zandy <[EMAIL PROTECTED]>. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/