user/sven/linux.git/lib/percpu-refcount.c, branch v4.1.2

percpu_ref: make INIT_ATOMIC and switch_to_atomic() sticky

2014-09-24T17:31:50Z

Currently, a percpu_ref which is initialized with PERPCU_REF_INIT_ATOMIC or switched to atomic mode via switch_to_atomic() automatically reverts to percpu mode on the first percpu_ref_reinit(). This makes the atomic mode difficult to use for cases where a percpu_ref is used as a persistent on/off switch which may be cycled multiple times. This patch makes such atomic state sticky so that it survives through kill/reinit cycles. After this patch, atomic state is cleared only by an explicit percpu_ref_switch_to_percpu() call. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet Cc: Jens Axboe Cc: Christoph Hellwig Cc: Johannes Weiner

percpu_ref: add PERCPU_REF_INIT_* flags

2014-09-24T17:31:50Z

With the recent addition of percpu_ref_reinit(), percpu_ref now can be used as a persistent switch which can be turned on and off repeatedly where turning off maps to killing the ref and waiting for it to drain; however, there currently isn't a way to initialize a percpu_ref in its off (killed and drained) state, which can be inconvenient for certain persistent switch use cases. Similarly, percpu_ref_switch_to_atomic/percpu() allow dynamic selection of operation mode; however, currently a newly initialized percpu_ref is always in percpu mode making it impossible to avoid the latency overhead of switching to atomic mode. This patch adds @flags to percpu_ref_init() and implements the following flags. * PERCPU_REF_INIT_ATOMIC : start ref in atomic mode * PERCPU_REF_INIT_DEAD : start ref killed and drained These flags should be able to serve the above two use cases. v2: target_core_tpg.c conversion was missing. Fixed. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet Cc: Jens Axboe Cc: Christoph Hellwig Cc: Johannes Weiner

percpu_ref: decouple switching to percpu mode and reinit

2014-09-24T17:31:49Z

percpu_ref has treated the dropping of the base reference and switching to atomic mode as an integral operation; however, there's nothing inherent tying the two together. The use cases for percpu_ref have been expanding continuously. While the current init/kill/reinit/exit model can cover a lot, the coupling of kill/reinit with atomic/percpu mode switching is turning out to be too restrictive for use cases where many percpu_refs are created and destroyed back-to-back with only some of them reaching extended operation. The coupling also makes implementing always-atomic debug mode difficult. This patch separates out percpu mode switching into percpu_ref_switch_to_percpu() and reimplements percpu_ref_reinit() on top of it. * DEAD still requires ATOMIC. A dead ref can't be switched to percpu mode w/o going through reinit. v2: __percpu_ref_switch_to_percpu() was missing static. Fixed. Reported by Fengguang aka kbuild test robot. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet Cc: Jens Axboe Cc: Christoph Hellwig Cc: Johannes Weiner Cc: kbuild test robot

percpu_ref: decouple switching to atomic mode and killing

2014-09-24T17:31:49Z

percpu_ref has treated the dropping of the base reference and switching to atomic mode as an integral operation; however, there's nothing inherent tying the two together. The use cases for percpu_ref have been expanding continuously. While the current init/kill/reinit/exit model can cover a lot, the coupling of kill/reinit with atomic/percpu mode switching is turning out to be too restrictive for use cases where many percpu_refs are created and destroyed back-to-back with only some of them reaching extended operation. The coupling also makes implementing always-atomic debug mode difficult. This patch separates out atomic mode switching into percpu_ref_switch_to_atomic() and reimplements percpu_ref_kill_and_confirm() on top of it. * The handling of __PERCPU_REF_ATOMIC and __PERCPU_REF_DEAD is now differentiated. Among get/put operations, percpu_ref_tryget_live() is the only one which cares about DEAD. * percpu_ref_switch_to_atomic() can be called multiple times on the same ref. This means that multiple @confirm_switch may get queued up which we can't do reliably without extra memory area. This is handled by making the later invocation synchronously wait for the completion of the previous one. This isn't particularly desirable but such synchronous waits shouldn't happen in most cases. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet Cc: Jens Axboe Cc: Christoph Hellwig Cc: Johannes Weiner

percpu_ref: add PCPU_REF_DEAD

2014-09-24T17:31:49Z

percpu_ref will be restructured so that percpu/atomic mode switching and reference killing are dedoupled. In preparation, add PCPU_REF_DEAD and PCPU_REF_ATOMIC_DEAD which is OR of ATOMIC and DEAD. For now, ATOMIC and DEAD are changed together and all PCPU_REF_ATOMIC uses are converted to PCPU_REF_ATOMIC_DEAD without causing any behavior changes. percpu_ref_init() now specifies an explicit alignment when allocating the percpu counters so that the pointer has enough unused low bits to accomodate the flags. Note that one flag was fine as min alignment for percpu memory is 2 bytes but two flags are already too many for the natural alignment of unsigned longs on archs like cris and m68k. v2: The original patch had BUILD_BUG_ON() which triggers if unsigned long's alignment isn't enough to accomodate the flags, which triggered on cris and m64k. percpu_ref_init() updated to specify the required alignment explicitly. Reported by Fengguang. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet Cc: kbuild test robot

percpu_ref: rename things to prepare for decoupling percpu/atomic mode switch

2014-09-24T17:31:48Z

percpu_ref will be restructured so that percpu/atomic mode switching and reference killing are dedoupled. In preparation, do the following renames. * percpu_ref->confirm_kill -> percpu_ref->confirm_switch * __PERCPU_REF_DEAD -> __PERCPU_REF_ATOMIC * __percpu_ref_alive() -> __ref_is_percpu() This patch is pure rename and doesn't introduce any functional changes. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet

percpu_ref: replace pcpu_ prefix with percpu_

2014-09-24T17:31:48Z

percpu_ref uses pcpu_ prefix for internal stuff and percpu_ for externally visible ones. This is the same convention used in the percpu allocator implementation. It works fine there but percpu_ref doesn't have too much internal-only stuff and scattered usages of pcpu_ prefix are confusing than helpful. This patch replaces all pcpu_ prefixes with percpu_. This is pure rename and there's no functional change. Note that PCPU_REF_DEAD is renamed to __PERCPU_REF_DEAD to signify that the flag is internal. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet

percpu_ref: minor code and comment updates

2014-09-24T17:31:48Z

* Some comments became stale. Updated. * percpu_ref_tryget() unnecessarily initializes @ret. Removed. * A blank line removed from percpu_ref_kill_rcu(). * Explicit function name in a WARN format string replaced with __func__. * WARN_ON() in percpu_ref_reinit() converted to WARN_ON_ONCE(). Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet

percpu_ref: relocate percpu_ref_reinit()

2014-09-24T17:31:48Z

percpu_ref is gonna go through restructuring. Move percpu_ref_reinit() after percpu_ref_kill_and_confirm(). This will make later changes easier to follow and result in cleaner organization. Signed-off-by: Tejun Heo Reviewed-by: Kent Overstreet

Revert "blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe"

2014-09-24T17:07:33Z

This reverts commit 0a30288da1aec914e158c2d7a3482a85f632750f, which was a temporary fix for SCSI blk-mq stall issue. The following patches will fix the issue properly by introducing atomic mode to percpu_ref. Signed-off-by: Tejun Heo Cc: Kent Overstreet Cc: Jens Axboe Cc: Christoph Hellwig