linux/kernel/exit.c, branch v5.5

Merge tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2020-01-03T19:17:14Z

Pull thread fixes from Christian Brauner: "Here are two fixes: - Panic earlier when global init exits to generate useable coredumps. Currently, when global init and all threads in its thread-group have exited we panic via: do_exit() -> exit_notify() -> forget_original_parent() -> find_child_reaper() This makes it hard to extract a useable coredump for global init from a kernel crashdump because by the time we panic exit_mm() will have already released global init's mm. We now panic slightly earlier. This has been a problem in certain environments such as Android. - Fix a race in assigning and reading taskstats for thread-groups with more than one thread. This patch has been waiting for quite a while since people disagreed on what the correct fix was at first" * tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: exit: panic before exit_mm() on global init exit taskstats: fix data-race

exit: panic before exit_mm() on global init exit

2019-12-21T15:48:01Z

Currently, when global init and all threads in its thread-group have exited we panic via: do_exit() -> exit_notify() -> forget_original_parent() -> find_child_reaper() This makes it hard to extract a useable coredump for global init from a kernel crashdump because by the time we panic exit_mm() will have already released global init's mm. This patch moves the panic futher up before exit_mm() is called. As was the case previously, we only panic when global init and all its threads in the thread-group have exited. Signed-off-by: chenqiwu Acked-by: Christian Brauner Acked-by: Oleg Nesterov [christian.brauner@ubuntu.com: fix typo, rewrite commit message] Link: https://lore.kernel.org/r/1576736993-10121-1-git-send-email-qiwuchen55@gmail.com Signed-off-by: Christian Brauner

Merge tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

2019-11-30T22:12:13Z

Pull pipe rework from David Howells: "This is my set of preparatory patches for building a general notification queue on top of pipes. It makes a number of significant changes: - It removes the nr_exclusive argument from __wake_up_sync_key() as this is always 1. This prepares for the next step: - Adds wake_up_interruptible_sync_poll_locked() so that poll can be woken up from a function that's holding the poll waitqueue spinlock. - Change the pipe buffer ring to be managed in terms of unbounded head and tail indices rather than bounded index and length. This means that reading the pipe only needs to modify one index, not two. - A selection of helper functions are provided to query the state of the pipe buffer, plus a couple to apply updates to the pipe indices. - The pipe ring is allowed to have kernel-reserved slots. This allows many notification messages to be spliced in by the kernel without allowing userspace to pin too many pages if it writes to the same pipe. - Advance the head and tail indices inside the pipe waitqueue lock and use wake_up_interruptible_sync_poll_locked() to poke poll without having to take the lock twice. - Rearrange pipe_write() to preallocate the buffer it is going to write into and then drop the spinlock. This allows kernel notifications to then be added the ring whilst it is filling the buffer it allocated. The read side is stalled because the pipe mutex is still held. - Don't wake up readers on a pipe if there was already data in it when we added more. - Don't wake up writers on a pipe if the ring wasn't full before we removed a buffer" * tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs: pipe: Remove sync on wake_ups pipe: Increase the writer-wakeup threshold to reduce context-switch count pipe: Check for ring full inside of the spinlock in pipe_write() pipe: Remove redundant wakeup from pipe_write() pipe: Rearrange sequence in pipe_write() to preallocate slot pipe: Conditionalise wakeup in pipe_read() pipe: Advance tail pointer inside of wait spinlock in pipe_read() pipe: Allow pipes to have kernel-reserved slots pipe: Use head and tail pointers for the ring, not cursor and length Add wake_up_interruptible_sync_poll_locked() Remove the nr_exclusive argument from __wake_up_sync_key() pipe: Reduce #inclusion of pipe_fs_i.h

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-11-27T00:02:40Z

Pull locking updates from Ingo Molnar: "The main changes in this cycle were: - A comprehensive rewrite of the robust/PI futex code's exit handling to fix various exit races. (Thomas Gleixner et al) - Rework the generic REFCOUNT_FULL implementation using atomic_fetch_* operations so that the performance impact of the cmpxchg() loops is mitigated for common refcount operations. With these performance improvements the generic implementation of refcount_t should be good enough for everybody - and this got confirmed by performance testing, so remove ARCH_HAS_REFCOUNT and REFCOUNT_FULL entirely, leaving the generic implementation enabled unconditionally. (Will Deacon) - Other misc changes, fixes, cleanups" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (27 commits) lkdtm: Remove references to CONFIG_REFCOUNT_FULL locking/refcount: Remove unused 'refcount_error_report()' function locking/refcount: Consolidate implementations of refcount_t locking/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions locking/refcount: Move saturation warnings out of line locking/refcount: Improve performance of generic REFCOUNT_FULL code locking/refcount: Move the bulk of the REFCOUNT_FULL implementation into the header locking/refcount: Remove unused refcount_*_checked() variants locking/refcount: Ensure integer operands are treated as signed locking/refcount: Define constants for saturation and max refcount values futex: Prevent exit livelock futex: Provide distinct return value when owner is exiting futex: Add mutex around futex exit futex: Provide state handling for exec() as well futex: Sanitize exit state handling futex: Mark the begin of futex exit explicitly futex: Set task::futex_state to DEAD right after handling futex exit futex: Split futex_mm_release() for exit/exec exit/exec: Seperate mm_release() futex: Replace PF_EXITPIDONE with a state ...

futex: Mark the begin of futex exit explicitly

2019-11-20T08:40:09Z

Instead of relying on PF_EXITING use an explicit state for the futex exit and set it in the futex exit function. This moves the smp barrier and the lock/unlock serialization into the futex code. As with the DEAD state this is restricted to the exit path as exec continues to use the same task struct. This allows to simplify that logic in a next step. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.539409004@linutronix.de

futex: Set task::futex_state to DEAD right after handling futex exit

2019-11-20T08:40:08Z

Setting task::futex_state in do_exit() is rather arbitrarily placed for no reason. Move it into the futex code. Note, this is only done for the exit cleanup as the exec cleanup cannot set the state to FUTEX_STATE_DEAD because the task struct is still in active use. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.439511191@linutronix.de

exit/exec: Seperate mm_release()

2019-11-20T08:40:08Z

mm_release() contains the futex exit handling. mm_release() is called from do_exit()->exit_mm() and from exec()->exec_mm(). In the exit_mm() case PF_EXITING and the futex state is updated. In the exec_mm() case these states are not touched. As the futex exit code needs further protections against exit races, this needs to be split into two functions. Preparatory only, no functional change. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.240518241@linutronix.de

futex: Replace PF_EXITPIDONE with a state

2019-11-20T08:40:07Z

The futex exit handling relies on PF_ flags. That's suboptimal as it requires a smp_mb() and an ugly lock/unlock of the exiting tasks pi_lock in the middle of do_exit() to enforce the observability of PF_EXITING in the futex code. Add a futex_state member to task_struct and convert the PF_EXITPIDONE logic over to the new state. The PF_EXITING dependency will be cleaned up in a later step. This prepares for handling various futex exit issues later. Signed-off-by: Thomas Gleixner Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20191106224556.149449274@linutronix.de

Remove the nr_exclusive argument from __wake_up_sync_key()

2019-10-23T16:02:34Z

Remove the nr_exclusive argument from __wake_up_sync_key() and derived functions as everything seems to set it to 1. Note also that if it wasn't set to 1, it would clear WF_SYNC anyway. Signed-off-by: David Howells Acked-by: Peter Zijlstra (Intel)

exit: use pid_has_task() in do_wait()

2019-10-17T13:36:58Z

Replace hlist_empty() with the new pid_has_task() helper which is more idiomatic, easier to grep for, and unifies how callers perform this check. Signed-off-by: Christian Brauner Reviewed-by: Oleg Nesterov Link: https://lore.kernel.org/r/20191017101832.5985-4-christian.brauner@ubuntu.com