diff options
| author | Andrea Righi <arighi@nvidia.com> | 2026-05-26 12:05:02 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-05-29 12:43:15 +0200 |
| commit | 4043f549841619a01999bf5d4e0b7931ef87f6cc (patch) | |
| tree | 064a763282049d8cd2688d12bca195c2f837bf3b /kernel/sched | |
| parent | 1eae219ea0e80eed83c129e8cae0f007843f1893 (diff) | |
sched/deadline: Reject debugfs dl_server writes for offline CPUs
Writing runtime or period via the per-CPU dl_server debugfs files
(/sys/kernel/debug/sched/{fair,ext}_server/cpu*/{runtime,period}) on an
offline CPU can trigger two distinct kernel issues:
1) Divide-by-zero in dl_server_apply_params():
Oops: divide error: 0000 [#1] SMP NOPTI
RIP: 0010:dl_server_apply_params+0x239/0x3a0
Call Trace:
sched_server_write_common.isra.0+0x21a/0x3c0
full_proxy_write+0x78/0xd0
vfs_write+0xe7/0x6e0
Both __dl_sub() and __dl_add() divide by cpus internally, which can be
0 once the CPU has been removed from any active root-domain span (this
has been latent since the debugfs interface was introduced).
2) WARN_ON_ONCE in dl_server_start():
WARNING: kernel/sched/deadline.c:1805 at dl_server_start+0x232/0x270
Commit ee6e44dfe6e5 ("sched/deadline: Stop dl_server before CPU goes
offline") added this check to catch enqueueing the server on an
offline rq.
There's no meaningful semantics for re-configuring the per-CPU dl_server
bandwidth while the CPU is offline, so simply reject the write with
-EBUSY so userspace gets a clear error.
Closes: https://lore.kernel.org/all/20260526092228.3B6891F00A3A@smtp.kernel.org/
Fixes: d741f297bcea ("sched/fair: Fair server interface")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: abaci-kreproducer <abaci@linux.alibaba.com>
Link: https://patch.msgid.link/20260526100502.575774-1-arighi@nvidia.com
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/debug.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index 4809e1d23081..5e09cf9fae3e 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -416,6 +416,9 @@ static ssize_t sched_server_write_common(struct file *filp, const char __user *u return -EINVAL; } + if (!cpu_online(cpu_of(rq))) + return -EBUSY; + update_rq_clock(rq); dl_server_stop(dl_se); retval = dl_server_apply_params(dl_se, runtime, period, 0); |