On 13.01.21 г. 14:09 ч., Christoph Hellwig wrote: > On Wed, Jan 13, 2021 at 01:41:09PM +0200, Nikolay Borisov wrote: >> >> >> On 13.01.21 ??. 13:27 ??., Christoph Hellwig wrote: >>> Pavel has looked into this before and got stuck on the allocator >>> workqueue offloads: >>> >>> [PATCH v13 0/4] xfs: Remove wrappers for some semaphores >> >> I haven't looked into his series but I fail to see how lifting >> rwsemaphore out of the nested structure can change the behavior ? It >> just removes a level of indirection. My patches are semantically >> identical to the original code. > > mrlocks have the mr_writer field that annotate that the is a writer > locking the lock. The XFS asserts use it to assert that the lock that > the current thread holds it for exclusive protection, which isn't > actually what the field says, and this breaks when XFS uses synchronous > execution of work_struct as basically an extension of the kernel stack. I'm still failing to see what's the problem of checking the last bit of the rwsem ->count field. It is set when the sem is held for writing (identical to what mr_write does). As I mention in the cover letter this might be considered a bit hacky because it exposes an internal detail of the rwsem i.e that the bit of interest is bit 0. But I believe the same can be achieved using lockdep_is_held_type(xx, 0/1) and making XFS's debug routines depend on lockdep being on. >
