On Fri, Jun 15, 2018 at 9:43 PM, John Hubbard <jhubbard@xxxxxxxxxx> wrote: > On 06/13/2018 12:51 PM, Dan Williams wrote: >> [ adding Andrew, Christoph, and linux-mm ] >> >> On Wed, Jun 13, 2018 at 12:33 PM, Joe Gorse <jhgorse@xxxxxxxxx> wrote: >>> Greetings, >>> >>> Please CC answers & comments to this email. Thanks! =) >>> >>> Our build is breaking as of >>> commit e7638488434415aa478e78435cac8f0365737638 >>> Author: Dan Williams <dan.j.williams@xxxxxxxxx> >>> Date: Wed May 16 11:46:08 2018 -0700 >>> >>> mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS >>> ... snip ... >>> https://patchwork.kernel.org/patch/10412459/ >>> >>> We do not directly use the GPL-only symbol '__put_devmap_managed_page'. It >>> appears to be picked up from static-inlining in put_page(), which we need. >>> >>> How shall we proceed? Would it be reasonable to request the change of the >>> GPL-only exports for this commit? >>> >>> Cheers, >>> Joe Gorse >>> >>> P.S. The build failure, for the morbidly curious: >>>> FATAL: modpost: GPL-incompatible module libafs.ko uses GPL-only symbol >>>> '__put_devmap_managed_page' >>>> scripts/Makefile.modpost:92: recipe for target '__modpost' failed >>>> make[6]: *** [__modpost] Error 1 >> >> I think the right answer here is to make __put_devmap_managed_page() >> EXPORT_SYMBOL(), since features like devm_memremap_pages() want to >> change the behavior of all users of put_page(). It again holds that >> devm_memremap_pages() needs to become EXPORT_SYMBOL_GPL() because it, >> not put_page(), is the interface that is leaking control of core >> kernel state/infrastructure to its users. >> > > Hi Dan and all, > > It looks like put_page() also picks up one more GPL symbol: > devmap_managed_key. > > put_page > put_devmap_managed_page > devmap_managed_key > > __put_devmap_managed_page > > > So if the goal is to restore put_page() to be effectively EXPORT_SYMBOL > again, then I think there would also need to be either a non-inlined > wrapper for devmap_managed_key (awkward for a static key), or else make > it EXPORT_SYMBOL, or maybe something else that's less obvious to me at the > moment. Right, certainly flipping the key is a kernel internal detail since it is giving the dev_pagemap owner purview over all kernel page events, but put_page() users are silent consumers. And you're right there's currently no good way I see to export the 'producer' and 'consumer' side of the key with different export types.
