Kristian Høgsberg wrote: > On Wed, Feb 18, 2009 at 12:36 PM, Eric Anholt <e...@anholt.net> wrote: > >> On Wed, 2009-02-18 at 11:02 -0500, k...@bitplanet.net wrote: >> >>> From: Kristian Høgsberg <k...@redhat.com> >>> >>> A number of GEM operations (and legacy drm ones) want to copy data to >>> or from userspace while holding the struct_mutex lock. However, the >>> fault handler calls us with the mmap_sem held and thus enforces the >>> opposite locking order. This patch downs the mmap_sem up front for >>> those operations that access userspace data under the struct_mutex >>> lock to ensure the locking order is consistent. >>> >>> Signed-off-by: Kristian Høgsberg <k...@redhat.com> >>> >> Have you tested this against actually faulting? My understanding was >> that you can't recurse on mmap_sem. >> > > I tested it and it worked, but didn't add code to detect contention so > I can't say for sure I hit that case. mmap_sem is a read/write > semaphore, so while we can't recurse, we can get away with taking two > reader locks. > > cheers, > Kristian > Kristian, This seems a bit odd to me. The extra lock taking does not prevent any deadlocks, so is this done to only silence a warning message? A reversed locking order between a mutex and an rwsem can never deadlock if the rwsem is only taken in read mode. If the mutex is taken simultaneously as the rwsem in _write_ mode then that locking order must be preserved across the code, even when the rwsem is taken in read mode.
/Thomas > ------------------------------------------------------------------------------ > Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA > -OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise > -Strategies to boost innovation and cut costs with open source participation > -Receive a $600 discount off the registration fee with the source code: SFAD > http://p.sf.net/sfu/XcvMzF8H > -- > _______________________________________________ > Dri-devel mailing list > Dri-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/dri-devel > ------------------------------------------------------------------------------ Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA -OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise -Strategies to boost innovation and cut costs with open source participation -Receive a $600 discount off the registration fee with the source code: SFAD http://p.sf.net/sfu/XcvMzF8H -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
