Try to be more explicit why the workqueue watchdog does not take
pool->lock by default. Spin locks are full memory barriers which
delay anything. Obviously, they would primary delay operations
on the related worker pools.

Explain why it is enough to prevent the false positive by re-checking
the timestamp under the pool->lock.

Finally, make it clear what would be the alternative solution in
__queue_work() which is a hotter path.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

On weakly ordered architectures (e.g., arm64), the lockless check in
wq_watchdog_timer_fn() can observe a reordering between the worklist
insertion and the last_progress_ts update. Specifically, the watchdog
can see a non-empty worklist (from a list_add) while reading a stale
last_progress_ts value, causing a false positive stall report.

This was confirmed by reading pool->last_progress_ts again after holding
pool->lock in wq_watchdog_timer_fn():

  workqueue watchdog: pool 7 false positive detected!
    lockless_ts=4784580465 locked_ts=4785033728
    diff=453263ms worklist_empty=0

To avoid slowing down the hot path (queue_work, etc.), recheck
last_progress_ts with pool->lock held. This will eliminate the false
positive with minimal overhead.

Remove two extra empty lines in wq_watchdog_timer_fn() as we are on it.

Fixes: 82607adcf9cd ("workqueue: implement lockup detector")
Cc: stable@vger.kernel.org # v4.5+
Assisted-by: claude-code:claude-opus-4-6
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

show_cpu_pool_hog() and show_cpu_pools_hogs() no longer only dump CPU
hogs — since commit 8823eaef45da ("workqueue: Show all busy workers in
stall diagnostics"), they dump every in-flight worker in the pool's
busy_hash.

Rename them to show_cpu_pool_busy_workers() and
show_cpu_pools_busy_workers() to accurately describe what they do.

Also fix the pr_info() message to say "stalled worker pools" instead of
"stalled CPU-bound worker pools", since sleeping/blocked workers are now
included.

No functional change.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

show_cpu_pool_hog() only prints workers whose task is currently running
on the CPU (task_is_running()).  This misses workers that are busy
processing a work item but are sleeping or blocked — for example, a
worker that clears PF_WQ_WORKER and enters wait_event_idle().  Such a
worker still occupies a pool slot and prevents progress, yet produces
an empty backtrace section in the watchdog output.

This is happening on real arm64 systems, where
toggle_allocation_gate() IPIs every single CPU in the machine (which
lacks NMI), causing workqueue stalls that show empty backtraces because
toggle_allocation_gate() is sleeping in wait_event_idle().

Remove the task_is_running() filter so every in-flight worker in the
pool's busy_hash is dumped.  The busy_hash is protected by pool->lock,
which is already held.

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

When diagnosing workqueue stalls, knowing how long each in-flight work
item has been executing is valuable. Add a current_start timestamp
(jiffies) to struct worker, set it when a work item begins execution in
process_one_work(), and print the elapsed wall-clock time in show_pwq().

Unlike current_at (which tracks CPU runtime and resets on wakeup for
CPU-intensive detection), current_start is never reset because the
diagnostic cares about total wall-clock time including sleeps.

Before: in-flight: 165:stall_work_fn [wq_stall]
After:  in-flight: 165:stall_work_fn [wq_stall] for 100s

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

The watchdog_ts name doesn't convey what the timestamp actually tracks.
This field tracks the last time a workqueue got progress.

Rename it to last_progress_ts to make it clear that it records when the
pool last made forward progress (started processing new work items).

No functional change.

Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

pr_cont_worker_id() checks pool->flags against WQ_BH, which is a
workqueue-level flag (defined in workqueue.h). Pool flags use a
separate namespace with POOL_* constants (defined in workqueue.c).
The correct constant is POOL_BH. Both WQ_BH and POOL_BH are defined
as (1 << 0) so this has no behavioral impact, but it is semantically
wrong and inconsistent with every other pool-level BH check in the
file.

Fixes: 4cb1ef64609f ("workqueue: Implement BH workqueues to eventually replace tasklets")
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

This is the exact same thing as the 'alloc_obj()' version, only much
smaller because there are a lot fewer users of the *alloc_flex()
interface.

As with alloc_obj() version, this was done entirely with mindless brute
force, using the same script, except using 'flex' in the pattern rather
than 'objs*'.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

This was done entirely with mindless brute force, using

    git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
        xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'

to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.

Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.

For the same reason the 'flex' versions will be done as a separate
conversion.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:

Single allocations:	kmalloc(sizeof(TYPE), ...)
are replaced with:	kmalloc_obj(TYPE, ...)

Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with:	kmalloc_objs(TYPE, COUNT, ...)

Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)

(where TYPE may also be *VAR)

The resulting allocations no longer return "void *", instead returning
"TYPE *".

Signed-off-by: Kees Cook <kees@kernel.org>