Messages in this thread Patch in this message | | | Date | Fri, 1 Jul 2022 22:20:24 +1000 | Subject | Re: [PATCH v7 2/4] kernfs: Change kernfs_notify_list to llist. | From | Imran Khan <> |
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Hello Marek,
On 1/7/22 9:22 pm, Marek Szyprowski wrote: > Hi All, > > On 15.06.2022 04:10, Imran Khan wrote: >> At present kernfs_notify_list is implemented as a singly linked >> list of kernfs_node(s), where last element points to itself and >> value of ->attr.next tells if node is present on the list or not. >> Both addition and deletion to list happen under kernfs_notify_lock. >> >> Change kernfs_notify_list to llist so that addition to list can heppen >> locklessly. >> >> Suggested by: Al Viro <viro@zeniv.linux.org.uk> >> Signed-off-by: Imran Khan <imran.f.khan@oracle.com> >> Acked-by: Tejun Heo <tj@kernel.org> > > This patch landed in linux next-20220630 as commit b8f35fa1188b > ("kernfs: Change kernfs_notify_list to llist."). Unfortunately, it > causes serious regression on my test systems. It can be easily noticed > in the logs by the following warning: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 34 at fs/kernfs/dir.c:531 kernfs_put.part.0+0x1a4/0x1d8 > kernfs_put: console/active: released with incorrect active_ref 0 > Modules linked in: > CPU: 1 PID: 34 Comm: kworker/1:4 Not tainted > 5.19.0-rc4-05465-g5732b42edfd1 #12317 > Hardware name: Samsung Exynos (Flattened Device Tree) > Workqueue: events kernfs_notify_workfn > unwind_backtrace from show_stack+0x10/0x14 > show_stack from dump_stack_lvl+0x40/0x4c > dump_stack_lvl from __warn+0xc8/0x13c > __warn from warn_slowpath_fmt+0x90/0xb4 > warn_slowpath_fmt from kernfs_put.part.0+0x1a4/0x1d8 > kernfs_put.part.0 from kernfs_notify_workfn+0x1a0/0x1d0 > kernfs_notify_workfn from process_one_work+0x1ec/0x4cc > process_one_work from worker_thread+0x58/0x54c > worker_thread from kthread+0xd0/0xec > kthread from ret_from_fork+0x14/0x2c > Exception stack(0xf099dfb0 to 0xf099dff8) > ... > ---[ end trace 0000000000000000 ]--- >
Thanks for reporting this issue. It has been reported earlier in [1] as well. I am unable to reproduce it locally. Could you please test with following patch on top of linux next-20220630 and let me know if it helps:
From 6bf7f1adc4b091dc6d6c60e0dd0f16247f61f374 Mon Sep 17 00:00:00 2001 From: Imran Khan <imran.f.khan@oracle.com> Date: Fri, 1 Jul 2022 14:27:52 +1000 Subject: [PATCH] kernfs: Avoid re-adding kernfs_node into kernfs_notify_list.
--- fs/kernfs/file.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index bb933221b4bae..e8ec054e11c63 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -917,6 +917,7 @@ static void kernfs_notify_workfn(struct work_struct *work) if (free == NULL) return;
+ free->next = NULL; attr = llist_entry(free, struct kernfs_elem_attr, notify_next); kn = attribute_to_node(attr, struct kernfs_node, attr); root = kernfs_root(kn); @@ -992,9 +993,11 @@ void kernfs_notify(struct kernfs_node *kn) rcu_read_unlock();
/* schedule work to kick fsnotify */ - kernfs_get(kn); - llist_add(&kn->attr.notify_next, &kernfs_notify_list); - schedule_work(&kernfs_notify_work); + if (kn->attr.notify_next.next != NULL) { + kernfs_get(kn); + llist_add(&kn->attr.notify_next, &kernfs_notify_list); + schedule_work(&kernfs_notify_work); + } } EXPORT_SYMBOL_GPL(kernfs_notify);
base-commit: 6cc11d2a1759275b856e464265823d94aabd5eaf -- 2.30.2
Thanks -- Imran
[1]: https://lore.kernel.org/lkml/0b3c1362-5f0d-44d5-d3e7-c01de59a4e86@oracle.com/
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