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BACKPORT: io_uring/fdinfo: remove need for sqpoll lock for thread/pid retrieval

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A previous commit added a trylock for getting the SQPOLL thread info via
fdinfo, but this introduced a regression where we often fail to get it if
the thread is busy. For that case, we end up not printing the current CPU
and PID info.

Rather than rely on this lock, just print the pid we already stored in
the io_sq_data struct, and ensure we update the current CPU every time
we've slept or potentially rescheduled. The latter won't potentially be
100% accurate, but that wasn't the case before either as the task can
get migrated at any time unless it has been pinned at creation time.

We retain keeping the io_sq_data dereference inside the ctx->uring_lock,
as it has always been, as destruction of the thread and data happen below
that. We could make this RCU safe, but there's little point in doing that.

With this, we always print the last valid information we had, rather than
have spurious outputs with missing information.

Bug: 254441685
Fixes: 7644b1a1c9 ("io_uring/fdinfo: lock SQ thread while retrieving thread cpu/pid")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit a0d45c3f596be53c1bd8822a1984532d14fdcea9)
[Lee: PF_NO_SETAFFINITY has been removed upstream causing surrounding diff to change]
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Iab4aeffb443ed5140b33dd7274fee57c36f40f9e
This commit is contained in:
Jens Axboe
2023-11-14 09:55:50 -07:00
committed by Treehugger Robot
parent 30c4764908
commit 7d59065aa4
2 changed files with 12 additions and 9 deletions
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9
io_uring/fdinfo.c
View File

@@ -141,13 +141,8 @@ static __cold void __io_uring_show_fdinfo(struct io_ring_ctx *ctx,
if (has_lock && (ctx->flags & IORING_SETUP_SQPOLL)) {
struct io_sq_data *sq = ctx->sq_data;
if (mutex_trylock(&sq->lock)) {
if (sq->thread) {
sq_pid = task_pid_nr(sq->thread);
sq_cpu = task_cpu(sq->thread);
}
mutex_unlock(&sq->lock);
}
sq_pid = sq->task_pid;
sq_cpu = sq->sq_cpu;
}
seq_printf(m, "SqThread:\t%d\n", sq_pid);

12
io_uring/sqpoll.c
View File

@@ -214,6 +214,7 @@ static bool io_sqd_handle_event(struct io_sq_data *sqd)
did_sig = get_signal(&ksig);
cond_resched();
mutex_lock(&sqd->lock);
sqd->sq_cpu = raw_smp_processor_id();
}
return did_sig || test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
}
@@ -229,10 +230,15 @@ static int io_sq_thread(void *data)
snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
set_task_comm(current, buf);
if (sqd->sq_cpu != -1)
/* reset to our pid after we've set task_comm, for fdinfo */
sqd->task_pid = current->pid;
if (sqd->sq_cpu != -1) {
set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
else
} else {
set_cpus_allowed_ptr(current, cpu_online_mask);
sqd->sq_cpu = raw_smp_processor_id();
}
current->flags |= PF_NO_SETAFFINITY;
mutex_lock(&sqd->lock);
@@ -262,6 +268,7 @@ static int io_sq_thread(void *data)
mutex_unlock(&sqd->lock);
cond_resched();
mutex_lock(&sqd->lock);
sqd->sq_cpu = raw_smp_processor_id();
}
continue;
}
@@ -295,6 +302,7 @@ static int io_sq_thread(void *data)
mutex_unlock(&sqd->lock);
schedule();
mutex_lock(&sqd->lock);
sqd->sq_cpu = raw_smp_processor_id();
}
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
atomic_andnot(IORING_SQ_NEED_WAKEUP,