Hi, the following patchset implements a killable variant of write lock for rw_semaphore. My usecase is to turn as many mmap_sem write users to use a killable variant which will be helpful for the oom_reaper [1] to asynchronously tear down the oom victim address space which requires mmap_sem for read. This will reduce a likelihood of OOM livelocks caused by oom victim being stuck on a lock or other resource which prevents it to reach its exit path and release the memory. I haven't implemented the killable variant of the read lock because I do not have any usecase for this API. The patchset is organized as follows. - Patch 1 is a trivial cleanup - Patch 2, I belive, shouldn't introduce any functional changes as per Documentation/memory-barriers.txt. - Patch 3 is the preparatory work and necessary infrastructure for down_write_killable. It implements generic __down_write_killable and prepares the write lock slow path to bail out earlier when told so - Patch 4-9 are implementing arch specific __down_write_killable. One patch per architecture. I haven't even tried to compile test anything but sparch which uses CONFIG_RWSEM_GENERIC_SPINLOCK in allnoconfig. Those shold be mostly trivial. - One exception is x86 which replaces the current implementation of __down_write with the generic one to make easier to read and get rid of one level of indirection to the slow path. More on that in patch 10. I do not have any problems to drop patch 10 and rework 11 to the current inline asm but I think the easier code would be better. - finally patch 11 implements down_write_killable and ties everything together. I am not really an expert on lockdep so I hope I got it right. Many of arch specific patches are basically same and I can squash them into one patch if this is preferred but I thought that one patch per arch is preferable. My patch to change mmap_sem write users to killable form is not part of the series because it is not finished yet but I guess it is not really necessary for the RFC. The API is used in the same way as mutex_lock_killable. I have tested on x86 with OOM situations with high mmap_sem contention (basically many parallel page faults racing with many parallel mmap/munmap tight loops) so the waiters for the write locks are routinely interrupted by SIGKILL. Patches should apply cleanly on both Linus and next tree. Any feedback is highly appreciated. --- [1] http://lkml.kernel.org/r/1452094975-551-1-git-send-email-mhocko@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
