On Wed, 17 Oct 2007, Jens Axboe wrote: > > That would hurt... Care to commit your for_each_sg() uglification fixup > for now then? Or disable the allocation debug config entry, so that the > sg+1 deref wont crash?
Well, in practice, it will only crash with DEBUG_PAGEALLOC, so few enough are going to be hit by it. In that sense I don't think we're in any deep trouble yet. That said, maybe this is an acceptable, if hacky, replacement for the current "for_each_sg()" loop. It does: - starts at one *before* the sglist - does the sg_next() at the *top* of the loop rather than the bottom of it - has a "--count" before that sg_next, so that we don't do it for the case when we break out and have used up all segments. Totally untested, but it *may* work, and it doesn't look horribly ugly. Ingo, does this actually make any difference? Linus --- include/linux/scatterlist.h | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 2dc7464..f5c8e11 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -51,11 +51,18 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg) return sg; } +static inline struct scatterlist *sg_safe_next(struct scatterlist *sg, int left) +{ + if (left < 0) + return NULL; + return sg_next(sg); +} + /* * Loop over each sg element, following the pointer to a new list if necessary */ #define for_each_sg(sglist, sg, nr, __i) \ - for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg)) + for (__i = (nr), sg = (sglist)-1; (sg = sg_safe_next(sg, --__i)) != NULL ; ) /** * sg_last - return the last scatterlist entry in a list - 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/