| Message ID | 20240316023443.101169-1-liu.yec@h3c.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v1] kdb: Fix the deadlock issue in KDB debugging. | expand |
^^^ This is v2 isn't it? On Sat, Mar 16, 2024 at 10:34:43AM +0800, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when transitioning out Please format the description correctly. > of the debugger and back to normal operation. This can cause > deadlock because schedule_work() is not NMI-safe. Wasn't there another paragraph to go here? : The stack trace below shows an example of the problem. In this : case the master cpu is not running from NMI but it has parked : the slave CPUs using an NMI and the parked CPUs is holding : spinlocks needed by schedule_work(). > example: > BUG: spinlock lockup suspected on CPU#0, namex/10450 > lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1 > ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000 > ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20 > Call Trace: > [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0 > [<ffffffff8147a7fc>] ? schedule+0x3c/0x90 > [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120 > [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10 > [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0 > [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20 > [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0 > [<ffffffff8108c540>] ? wake_up_q+0x70/0x70 > [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0 > [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75 > CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1 > Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019 > 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000 > ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980 > 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0 > Call Trace: > <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2 > [<ffffffff810a7f7f>] spin_dump+0x7f/0x100 > [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150 > [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20 > [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0 > [<ffffffff8108c4c5>] wake_up_process+0x15/0x20 > [<ffffffff8107b371>] insert_work+0x81/0xc0 > [<ffffffff8107b4e5>] __queue_work+0x135/0x390 > [<ffffffff8107b786>] queue_work_on+0x46/0x90 > [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70 > [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610 > [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0 > [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0 > [<ffffffff81054eb5>] kgdb_notify+0x35/0x70 > [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70 > [<ffffffff8108304d>] notify_die+0x3d/0x50 > [<ffffffff81017219>] do_int3+0x89/0x120 > [<ffffffff81480fb4>] int3+0x44/0x80 > > Suggested-by: daniel.thompson@linaro.org Thanks for the credit but I think the following is probably a better way to express it: Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Daniel.
On Thu, Mar 21, 2024 at 10:26:04AM +0800, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). > > example: > BUG: spinlock lockup suspected on CPU#0, namex/10450 > lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1 > ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000 > ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20 > Call Trace: > [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0 > [<ffffffff8147a7fc>] ? schedule+0x3c/0x90 > [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120 > [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10 > [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0 > [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20 > [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0 > [<ffffffff8108c540>] ? wake_up_q+0x70/0x70 > [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0 > [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75 > CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1 > Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019 > 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000 > ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980 > 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0 > Call Trace: > <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2 > [<ffffffff810a7f7f>] spin_dump+0x7f/0x100 > [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150 > [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20 > [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0 > [<ffffffff8108c4c5>] wake_up_process+0x15/0x20 > [<ffffffff8107b371>] insert_work+0x81/0xc0 > [<ffffffff8107b4e5>] __queue_work+0x135/0x390 > [<ffffffff8107b786>] queue_work_on+0x46/0x90 > [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70 > [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610 > [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0 > [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0 > [<ffffffff81054eb5>] kgdb_notify+0x35/0x70 > [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70 > [<ffffffff8108304d>] notify_die+0x3d/0x50 > [<ffffffff81017219>] do_int3+0x89/0x120 > [<ffffffff81480fb4>] int3+0x44/0x80 > > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > --- > drivers/tty/serial/kgdboc.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c > index 7ce7bb164..161b25ecc 100644 > --- a/drivers/tty/serial/kgdboc.c > +++ b/drivers/tty/serial/kgdboc.c > @@ -22,6 +22,7 @@ > #include <linux/module.h> > #include <linux/platform_device.h> > #include <linux/serial_core.h> > +#include <linux/irq_work.h> > > #define MAX_CONFIG_LEN 40 > > @@ -99,10 +100,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy) > > static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper); > > +static void kgdboc_queue_restore_input_helper(struct irq_work *unused) > +{ > + schedule_work(&kgdboc_restore_input_work); > +} > + > +static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper); > + > static void kgdboc_restore_input(void) > { > if (likely(system_state == SYSTEM_RUNNING)) > - schedule_work(&kgdboc_restore_input_work); > + irq_work_queue(&kgdboc_restore_input_irq_work); > } > > static int kgdboc_register_kbd(char **cptr) > @@ -133,6 +141,7 @@ static void kgdboc_unregister_kbd(void) > i--; > } > } > + irq_work_sync(&kgdboc_restore_input_irq_work); > flush_work(&kgdboc_restore_input_work); > } > #else /* ! CONFIG_KDB_KEYBOARD */ > -- > 2.25.1 > > Hi, This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him a patch that has triggered this response. He used to manually respond to these common problems, but in order to save his sanity (he kept writing the same thing over and over, yet to different people), I was created. Hopefully you will not take offence and will fix the problem in your patch and resubmit it so that it can be accepted into the Linux kernel tree. You are receiving this message because of the following common error(s) as indicated below: - This looks like a new version of a previously submitted patch, but you did not list below the --- line any changes from the previous version. Please read the section entitled "The canonical patch format" in the kernel file, Documentation/process/submitting-patches.rst for what needs to be done here to properly describe this. If you wish to discuss this problem further, or you have questions about how to resolve this issue, please feel free to respond to this email and Greg will reply once he has dug out from the pending patches received from other developers. thanks, greg k-h's patch email bot
> The stack trace below shows an example of the problem. In this case > the master cpu is not running from NMI but it has parked the slave > CPUs using an NMI and the parked CPUs is holding spinlocks needed by > schedule_work(). Add description information > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Add Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
On Thu, Mar 21, 2024 at 07:57:28AM +0000, Liuye wrote: > > > The stack trace below shows an example of the problem. In this case > > the master cpu is not running from NMI but it has parked the slave > > CPUs using an NMI and the parked CPUs is holding spinlocks needed by > > schedule_work(). > > Add description information > > > Signed-off-by: LiuYe <liu.yeC@h3c.com> > > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > > Add > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> I assume this reply is summarizing what changed between the previous version and v3? The best way to add the changelog requested by Greg's bot is to send a corrected v4 version. If you follow the example in https://docs.kernel.org/process/submitting-patches.html#the-canonical-patch-format then you'll see that what is expected. You can use git-notes to handle this. If you add a note containing something like the following: ~~~ Changes in v4: * Provide these changelogs. Changes in v3: * <please describe changes> Changes in v2: * <please describe changes> ~~~ Once you have the note than git-format-patch --notes will automatically included the changelog with the patch. Daniel. PS I know that v2 was circulated with an incorrect subject line but I think it is probably OK to call it v2 anyway... it makes the changelog clearer!
On 21. 03. 24, 12:50, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). I am missing here an explanation (perhaps because I cannot find any docs for irq_work) why irq_work works in this case. And why you need to schedule another work in the irq_work and not do the job directly. thanks,
>On 21. 03. 24, 12:50, liu.yec@h3c.com wrote: >> From: LiuYe <liu.yeC@h3c.com> >> >> Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will attempt >> to use schedule_work() to provoke a keyboard reset when transitioning >> out of the debugger and back to normal operation. >> This can cause deadlock because schedule_work() is not NMI-safe. >> >> The stack trace below shows an example of the problem. In this case >> the master cpu is not running from NMI but it has parked the slave >> CPUs using an NMI and the parked CPUs is holding spinlocks needed by >> schedule_work(). > >I am missing here an explanation (perhaps because I cannot find any docs for irq_work) why irq_work works in this case. Just need to postpone schedule_work to the slave CPU exiting the NMI context, and there will be no deadlock problem. irq_work will only respond to handle schedule_work after master cpu exiting the current interrupt context. When the master CPU exits the interrupt context, other CPUs will naturally exit the NMI context, so there will be no deadlock. >And why you need to schedule another work in the irq_work and not do the job directly. In the function kgdboc_restore_input_helper , use mutex_lock for protection. The mutex lock cannot be used in interrupt context. Guess that the process needs to run in the context of the process. Therefore, call schedule_work in irq_work. Keep the original flow unchanged.
On Fri, Mar 22, 2024 at 07:50:54AM +0000, Liuye wrote: > >On 21. 03. 24, 12:50, liu.yec@h3c.com wrote: > >> From: LiuYe <liu.yeC@h3c.com> > >> > >> Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will attempt > >> to use schedule_work() to provoke a keyboard reset when transitioning > >> out of the debugger and back to normal operation. > >> This can cause deadlock because schedule_work() is not NMI-safe. > >> > >> The stack trace below shows an example of the problem. In this case > >> the master cpu is not running from NMI but it has parked the slave > >> CPUs using an NMI and the parked CPUs is holding spinlocks needed by > >> schedule_work(). > > > > I am missing here an explanation (perhaps because I cannot find any > > docs for irq_work) why irq_work works in this case. > > Just need to postpone schedule_work to the slave CPU exiting the NMI > context, and there will be no deadlock problem. irq_work will only > respond to handle schedule_work after master cpu exiting the current > interrupt context. When the master CPU exits the interrupt context, > other CPUs will naturally exit the NMI context, so there will be no > deadlock. > > > And why you need to schedule another work in the irq_work and not do > > the job directly. > > In the function kgdboc_restore_input_helper , use mutex_lock for > protection. It is the call to input_register_handler() that forces us not to do the work from irq_work's hardirq callback. It is true that there are mutexes in kgdboc_restore_input_helper() but if they were the only problem we could change the locking strategy. > The mutex lock cannot be used in interrupt context. Guess > that the process needs to run in the context of the process. > Therefore, call schedule_work in irq_work. Keep the original flow > unchanged. You should answer these questions by posting a v5 with the explanation in the patch description (otherwise the explanation of how the fix works doesn't end up in the changelog). Daniel.
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 7ce7bb164..161b25ecc 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -22,6 +22,7 @@ #include <linux/module.h> #include <linux/platform_device.h> #include <linux/serial_core.h> +#include <linux/irq_work.h> #define MAX_CONFIG_LEN 40 @@ -99,10 +100,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy) static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper); +static void kgdboc_queue_restore_input_helper(struct irq_work *unused) +{ + schedule_work(&kgdboc_restore_input_work); +} + +static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper); + static void kgdboc_restore_input(void) { if (likely(system_state == SYSTEM_RUNNING)) - schedule_work(&kgdboc_restore_input_work); + irq_work_queue(&kgdboc_restore_input_irq_work); } static int kgdboc_register_kbd(char **cptr) @@ -133,6 +141,7 @@ static void kgdboc_unregister_kbd(void) i--; } } + irq_work_sync(&kgdboc_restore_input_irq_work); flush_work(&kgdboc_restore_input_work); } #else /* ! CONFIG_KDB_KEYBOARD */