On 2012-02-21, at 9:36 AM, Eric Sandeen wrote: > On 02/21/2012 07:55 AM, Xi Wang wrote: >> On Feb 20, 2012, at 6:47 PM, Eric Sandeen wrote: >>> Hm this raises a few questions I think. >>> >>> On the one hand, making sure the kmalloc arg doesn't overflow here is >>> certainly a good thing and probably the right thing to do in the short term. >>> >>> So I guess: >>> >>> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx> >>> >>> for that, to close the hole. >> >> Another possibility is to wait for knalloc/kmalloc_array in the -mm >> tree, which is basically the non-zeroing version of kcalloc that >> performs overflow checking. >> >>> Doesn't this also mean that a valid s_log_groups_per_flex (i.e. 31) >>> will fail in this resize code? That would be an unexpected outcome. >>> 2^31 groups per flex is a little crazy, but still technically valid >>> according to the limits in the code. >> >> Or we could limit s_log_groups_per_flex/groups_per_flex to a >> reasonable upper bound in ext4_fill_flex_info(), right? > > Depends on the "flex_bg" design intent, I guess. > > I don't know if the 2^31 was an intended design limit, or just a > mathematical limit that based on container sizes etc... > > I'd have to look at the resize code more carefully but I can't imagine > that it's imperative to allocate this stuff all at once. We previously tried to use a large flex_bg size to put all metadata into a single group so it could easily be allocated on a separate SSD device, but that didn't work very well. Once the number of bitmaps in group 0 is more than the number of free blocks in that group (below 16k groups, due to group descriptors) then they need to overflow into group 1 and collide with the group descriptors there. Then mke2fs chokes, AFAIR. It may be different with bigalloc, since the number of blocks in a group can be very large, I haven't tried that. In any case, I don't think anyone expects vmalloc(2^32 * struct size) to work, but I wouldn't sweat fixing this until there is some real reason to do so. Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
