Hi On Tue, Jun 17, 2014 at 11:54 AM, Florian Weimer <fweimer@xxxxxxxxxx> wrote: > On 06/13/2014 05:33 PM, David Herrmann wrote: >> >> On Fri, Jun 13, 2014 at 5:17 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> wrote: >>> >>> Isn't the point of SEAL_SHRINK to allow servers to mmap and read >>> safely without worrying about SIGBUS? >> >> >> No, I don't think so. >> The point of SEAL_SHRINK is to prevent a file from shrinking. SIGBUS >> is an effect, not a cause. It's only a coincidence that "OOM during >> reads" and "reading beyond file-boundaries" has the same effect: >> SIGBUS. >> We only protect against reading beyond file-boundaries due to >> shrinking. Therefore, OOM-SIGBUS is unrelated to SEAL_SHRINK. >> >> Anyone dealing with mmap() _has_ to use mlock() to protect against >> OOM-SIGBUS. Making SEAL_SHRINK protect against OOM-SIGBUS would be >> redundant, because you can achieve the same with SEAL_SHRINK+mlock(). > > > I don't think this is what potential users expect because mlock requires > capabilities which are not available to them. > > A couple of weeks ago, sealing was to be applied to anonymous shared memory. > Has this changed? Why should *reading* it trigger OOM? The file might have holes, therefore, you'd have to allocate backing pages. This might hit a soft-limit and fail. To avoid this, use fallocate() to allocate pages prior to mmap() or mlock() to make the kernel lock them in memory. Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
