Messages in this thread | | | Date | Sat, 29 Jul 2006 09:14:19 -0400 | From | Neil Horman <> | Subject | Re: [KJ] audit return code handling for kernel_thread [2/11] |
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On Sat, Jul 29, 2006 at 10:37:04AM +0100, Russell King wrote: > On Fri, Jul 28, 2006 at 04:07:13PM -0400, nhorman@tuxdriver.com wrote: > > Audit/Cleanup of kernel_thread calls, specifically checking of return codes. > > Problems seemed to fall into 3 main categories: > > > > 1) callers of kernel_thread were inconsistent about meaning of a zero return > > code. Some callers considered a zero return code to mean success, others took > > it to mean failure. a zero return code, while not actually possible in the > > current implementation, should be considered a success (pid 0 is/should be > > valid). fixed all callers to treat zero return as success > > > > 2) caller of kernel_thread saved return code of kernel_thread for later use > > without ever checking its value. Callers who did this tended to assume a > > non-zero return was success, and would often wait for a completion queue to be > > woken up, implying that an error (negative return code) from kernel_thread could > > lead to deadlock. Repaired by checking return code at call time, and setting > > saved return code to zero in the event of an error. > > This is inconsistent with your assertion that pid 0 "is/should be valid" > above. If you want '0' to mean "not valid" then it's not a valid return > value from kernel_thread() (and arguably that's true, since pid 0 is > permanently allocated to the idle thread.) > No its, not, but I can see how my comments might be ambiguous. I want zero to be a valid return code, since we never actually return zero, but we certainly could if we wanted to. Note that kernel_thread returns an int (not an unsigned int), and as such assuming that a non-zero return code implies success ignores the fact that kernel_thread can return a negative value, which indicates failure. This is what I found, and what my patch fixes.
> I don't particularly care whether you decide to that returning pid 0 from > kernel_thread is valid or not, just that your two points above are at least > consistent with each other. > My comments in (2) should be made more clear by changing "assume a non-zero return was success" to "assume a negative return was success". This is what my patch fixes.
Thanks & Regards Neil
> -- > Russell King > Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ > maintainer of: 2.6 Serial core - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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