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Date: Thu, 27 Oct 2022 18:58:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Stephen Boyd <sboyd@...nel.org>
Subject: Re: [RFC][PATCH v2 00/31] timers: Use del_timer_shutdown() before
freeing timers
On Thu, 27 Oct 2022 15:24:04 -0700
Guenter Roeck <linux@...ck-us.net> wrote:
> On Thu, Oct 27, 2022 at 11:05:25AM -0400, Steven Rostedt wrote:
> >
> > Back in April, I posted an RFC patch set to help mitigate a common issue
> > where a timer gets armed just before it is freed, and when the timer
> > goes off, it crashes in the timer code without any evidence of who the
> > culprit was. I got side tracked and never finished up on that patch set.
> > Since this type of crash is still our #1 crash we are seeing in the field,
> > it has become a priority again to finish it.
> >
> > This is v2 of that patch set. Thomas Gleixner posted an untested version
> > that makes timer->function NULL as the flag that it is shutdown. I took that
> > code, tested it (fixed it up), added more comments, and changed the
> > name to del_timer_shutdown() as Linus had asked. I also converted it to use
> > WARN_ON_ONCE() instead of just WARN_ON() as Linus asked for that too.
> >
>
> Here are various warnings and crashes. Complete logs are at
>
> https://kerneltests.org/builders
>
> in the "testing" column of the qemu test results.
>
> This is with the published patch set plus the fixups in
> timer_fixup_init() and timer_fixup_free().
>
> Guenter
>
> ---
> Block code:
>
> WARNING: CPU: 0 PID: 8 at lib/debugobjects.c:502 debug_print_object+0x66/0x7a
> ODEBUG: free active (active state 0) object type: timer_list hint: blk_rq_timed_out_timer+0x0/0xc
This is probably just missing a switch to shutdown.
>
> ---
> In tcp:
>
> WARNING: CPU: 0 PID: 255 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: free active (active state 0) object type: timer_list hint: tcp_keepalive_timer+0x0/0x3a8
>
> WARNING: CPU: 0 PID: 255 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: free active (active state 0) object type: timer_list hint: tcp_write_timer+0x0/0x1a8
Looking at these, I think the del_timer_try_shutdown() needs to always
shutdown (let's try that, and see if that fixes things before we rename
anything).
>
> ---
> Other networking:
>
> WARNING: CPU: 0 PID: 8 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: free active (active state 0) object type: timer_list hint: neigh_timer_handler+0x0/0x468
>
> ---
>
> WARNING: CPU: 0 PID: 280 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: init active (active state 0) object type: timer_list hint: tulip_timer+0x0/0x38
>
> That one is often followed by:
>
> [ 29.833216] ODEBUG: init active (active state 0) object type: timer_list hint: 0x0
> [ 29.833723] WARNING: CPU: 0 PID: 365 at lib/debugobjects.c:502 debug_print_object+0xb8/0x100
>
> in the same code line, suggesting that the timer may be shut down
> more than once (?). Then there is another crash with
>
> [ 29.863890] Insufficient stack space to handle exception!
> [ 29.863939] ESR: 0x0000000096000047 -- DABT (current EL)
> [ 29.863952] FAR: 0xffff800008b17f80
> [ 29.863959] Task stack: [0xffff800008b18000..0xffff800008b1c000]
> [ 29.863967] IRQ stack: [0xffff800008000000..0xffff800008004000]
> [ 29.863975] Overflow stack: [0xffff30a35fe7a0f0..0xffff30a35fe7b0f0]
> [ 29.863987] CPU: 0 PID: 365 Comm: ip Tainted: G W N 6.1.0-rc2-00138-gced58c742836 #1
> [ 29.863999] Hardware name: linux,dummy-virt (DT)
>
> followed by a sequence of
>
> [ 29.864572] __try_to_del_timer_sync+0x40/0xdc
> [ 29.864582] __del_timer_sync+0xa4/0x100
> [ 29.864590] timer_fixup_init+0x2c/0x5c
> [ 29.864599] __debug_object_init+0x248/0x53c
> [ 29.864606] debug_object_init+0x24/0x30
> [ 29.864614] timer_fixup_init+0x40/0x5c
> [ 29.864622] __debug_object_init+0x248/0x53c
> [ 29.864630] debug_object_init+0x24/0x30
> [ 29.864637] timer_fixup_init+0x40/0x5c
> [ 29.864645] __debug_object_init+0x248/0x53c
> [ 29.864658] debug_object_init+0x24/0x30
> [ 29.864666] timer_fixup_init+0x40/0x5c
> ...
> [ 29.866492] debug_object_init+0x24/0x30
> [ 29.866500] init_timer_key+0x7c/0x80
> [ 29.866508] tulip_down+0x1d0/0x24c
> [ 29.866518] tulip_close+0x3c/0xc0
>
> This crash is seen with variants on several platforms/architectures.
Hmm, I'll have to take a deeper look here.
>
> ---
>
> WARNING: CPU: 0 PID: 8 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: free active (active state 0) object type: timer_list hint: addrconf_dad_work+0x0/0x628
Hmm, I was afraid of this one.
Looks to be from the workqueue code for delayed work. I don't see a place
that frees besides just flushing it. And we can't determine if a flush is
permanent or will be armed again.
May need to add a helper function that resets the debugging so that it
doesn't trigger on delayed work timers. There's a DEBUG_OBJECTS_WORK that
handles bad work queue issues.
>
> ---
> mips64:
>
> WARNING: CPU: 0 PID: 280 at lib/debugobjects.c:502 debug_print_object+0xa4/0xd8
> ODEBUG: init active (active state 0) object type: timer_list hint: 0x0
Not a very good hint.
> Modules linked in:
> CPU: 0 PID: 280 Comm: ip Tainted: G W N 6.1.0-rc2-00138-gced58c742836 #1
> Stack : 0000000000000056 ffffffffffffffff 0000000000000008 00b65275abba8126
> 00b65275abba8126 0000000000000000 9000000004193728 ffffffff80f29f38
> ffffffff8105c9d8 ffffffffffff8880 9000000004193668 0000000000000000
> 0000000000000005 0000000000000010 ffffffff80c731a0 ffffffff81030000
> 2020205720202020 ffffffff81030000 0000000000000000 ffffffff80f29f38
> 0000000000000009 00000000000001f6 ffffffff8063d45c ffffffff81cb94c0
> ffffffff81d76240 0000000000000000 ffffffff807575a8 0000000000000000
> ffffffff81230000 9000000004190000 9000000004193720 9000000018002030
> ffffffff80c8f528 0000000000000000 0000000000000000 00b65275abba8126
> ffffffff8122e050 000000001000a4e1 ffffffff8010a884 00b65275abba8126
> ...
> Call Trace:
> [<ffffffff8010a884>] show_stack+0x3c/0x120
> [<ffffffff80c8f528>] dump_stack_lvl+0x4c/0x90
> [<ffffffff80130e54>] __warn+0xdc/0x1c8
> [<ffffffff80c75a08>] warn_slowpath_fmt+0x98/0xc4
> [<ffffffff8063d45c>] debug_print_object+0xa4/0xd8
> [<ffffffff8063e590>] __debug_object_init+0x2d0/0x670
> [<ffffffff801b44b8>] timer_fixup_init+0x40/0x58
>
> irq event stamp: 1537
> hardirqs last enabled at (1549): [<ffffffff8018e67c>] __up_console_sem+0x9c/0xc8
> hardirqs last disabled at (1560): [<ffffffff8018e658>] __up_console_sem+0x78/0xc8
> softirqs last enabled at (1324): [<ffffffff80a572bc>] dev_deactivate_many+0x32c/0x458
> softirqs last disabled at (1322): [<ffffffff80a57288>] dev_deactivate_many+0x2f8/0x458
> ---[ end trace 0000000000000000 ]---
>
> =====================================
> WARNING: bad unlock balance detected!
> 6.1.0-rc2-00138-gced58c742836 #1 Tainted: G W N
> -------------------------------------
> �������␈␂/-1 is trying to release lock (&obj_hash[i].lock) at:
> [<ffffffff801b41e0>] __try_to_del_timer_sync+0x48/0x140
> but there are no more locks to release!
>
> other info that might help us debug this:
> qemu-system-mips64: terminating on signal 15 from pid 2525787 (/bin/bash)
>
> ---
> Openrisc fails completely. Lots of the following, then boot stalls.
>
> WARNING: CPU: 0 PID: 88 at lib/debugobjects.c:502 debug_print_object+0xc0/0xe8
> ODEBUG: init active (active state 0) object type: timer_list hint: 0x0
> Modules linked in:
> CPU: 0 PID: 88 Comm: udhcpc Not tainted 6.1.0-rc2-00138-gced58c742836 #1
> Call trace:
> [<8eaa3f51>] dump_stack_lvl+0x44/0x80
> [<4da6c5ef>] dump_stack+0x1c/0x2c
> [<1b9f58b7>] __warn+0xdc/0x118
> [<86d4d066>] ? debug_print_object+0xc0/0xe8
> [<689beae8>] warn_slowpath_fmt+0x78/0x90
> [<86d4d066>] debug_print_object+0xc0/0xe8
> [<872f4074>] __debug_object_init+0x2bc/0x7f4
> [<c30d6214>] ? _raw_spin_unlock_irqrestore+0x50/0x84
> [<c3f3be91>] ? debug_check_no_locks_freed+0xb8/0x194
> [<558675c1>] ? slob_alloc+0xe8/0x350
> [<26225550>] ? lockdep_init_map_type+0x68/0x38c
> [<c3f3be91>] ? debug_check_no_locks_freed+0xb8/0x194
> [<2c9cf7b5>] ? inet_create+0x2e8/0x404
> [<bab055df>] debug_object_init+0x30/0x40
> [<6d2e468f>] init_timer_key+0xb4/0x110
> [<60c0d3e7>] ? sk_init_common+0x1a0/0x1c0
> [<b52686c2>] sock_init_data+0x60/0x2a4
> [<1ff904c3>] ? sk_alloc+0xe8/0x138
> [<ca3e6ef9>] inet_create+0x1e0/0x404
> [<623d726a>] ? inet_create+0x80/0x404
> [<a3256728>] ? lock_release+0x1c0/0x30c
> [<960a454e>] __sock_create+0x140/0x288
> [<0290cd64>] ? __sock_create+0x98/0x288
> [<b62bc649>] __sys_socket+0x7c/0x128
> [<fa003224>] ? do_work_pending+0x4c/0x118
> [<705147e9>] sys_socket+0x14/0x24
> [<9c4e015d>] ? _syscall_return+0x0/0x4
> ---[ end trace 0000000000000000 ]---
>
> ---
> parisc crashes.
>
> [ 3.015186] ------------[ cut here ]------------
> [ 3.015580] ODEBUG: init active (active state 0) object type: timer_list hint: timeout_waiting_on_port+0x0/0x2c
> [ 3.016945] WARNING: CPU: 0 PID: 1 at lib/debugobjects.c:502 debug_print_object+0x98/0xc8
> ...
> [ 3.026117] ODEBUG: init active (active state 0) object type: timer_list hint: 0x0
> [ 3.026355] WARNING: CPU: 0 PID: 1 at lib/debugobjects.c:502 debug_print_object+0x98/0xc8
> ...
> [ many more of the same ]
>
> [ 3.054542] stackcheck: swapper/0 will most likely overflow irq stack (sp:11e51800, stk bottom-top:11460004-11468004)
> [ 3.054592] Kernel panic - not syncing: low stack detected by irq handler - check messages
>
> and boom.
>
> ---
> usb:
>
> [ 23.993737] WARNING: CPU: 0 PID: 343 at lib/debugobjects.c:502 debug_print_object+0xac/0xc8
> [ 23.993953] ODEBUG: free active (active state 0) object type: timer_list hint: hub_init_func2+0x0/0xc
Yeah, there's going to be lots of these.
>
> ---
> ppc:
>
> [ 6.607478][ T1] ODEBUG: init active (active state 0) object type: timer_list hint: .ibmvscsi_timeout+0x0/0x58
> [ 6.608536][ T1] WARNING: CPU: 0 PID: 1 at lib/debugobjects.c:502 .debug_print_object+0xbc/0xf0
>
> followed by several of
>
> [ 6.623661][ T1] ODEBUG: init active (active state 0) object type: timer_list hint: 0x0
> [ 6.624155][ T1] WARNING: CPU: 0 PID: 1 at lib/debugobjects.c:502 .debug_print_object+0xbc/0xf0
>
> and finally:
>
> [ 6.694785][ C0] BUG: Kernel NULL pointer dereference on read at 0x000000b8
> [ 6.694796][ C0] Faulting instruction address: 0xc0000000001ece44
> [ 6.694807][ C0] Thread overran stack, or stack corrupted
> [ 6.694967][ C0] Oops: Kernel access of bad area, sig: 7 [#1]
Anyway, this is all an issue with the last patch that makes calling
shutdown a requirement before freeing and not just a hint.
You may want to test all but the last patch, as only the last patch is
what's going to trigger all the above, as it modifies the semantics of
DEBUG_OBJECTS_TIMER.
But for the tcp one, add this to the queue and see if the tcp one goes away?
-- Steve
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ecf625378078..e9838ce6a6cd 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1255,7 +1255,7 @@ int __del_timer(struct timer_list *timer, bool free)
if (timer_pending(timer)) {
base = lock_timer_base(timer, &flags);
ret = detach_if_pending(timer, base, true);
- if (free && ret) {
+ if (free) {
timer->function = NULL;
debug_timer_deactivate(timer);
}
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