| Message ID | 20170607162412.8432-1-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/06/17 18:24, Juergen Gross wrote: > There has been a report about a deadlock in the xenbus driver: > > [ 247.979498] ====================================================== > [ 247.985688] WARNING: possible circular locking dependency detected > [ 247.991882] 4.12.0-rc4-00022-gc4b25c0 #575 Not tainted > [ 247.997040] ------------------------------------------------------ > [ 248.003232] xenbus/91 is trying to acquire lock: > [ 248.007875] (&u->msgbuffer_mutex){+.+.+.}, at: [<ffff00000863e904>] > xenbus_dev_queue_reply+0x3c/0x230 > [ 248.017163] > [ 248.017163] but task is already holding lock: > [ 248.023096] (xb_write_mutex){+.+...}, at: [<ffff00000863a940>] > xenbus_thread+0x5f0/0x798 > [ 248.031267] > [ 248.031267] which lock already depends on the new lock. > [ 248.031267] > [ 248.039615] > [ 248.039615] the existing dependency chain (in reverse order) is: > [ 248.047176] > [ 248.047176] -> #1 (xb_write_mutex){+.+...}: > [ 248.052943] __lock_acquire+0x1728/0x1778 > [ 248.057498] lock_acquire+0xc4/0x288 > [ 248.061630] __mutex_lock+0x84/0x868 > [ 248.065755] mutex_lock_nested+0x3c/0x50 > [ 248.070227] xs_send+0x164/0x1f8 > [ 248.074015] xenbus_dev_request_and_reply+0x6c/0x88 > [ 248.079427] xenbus_file_write+0x260/0x420 > [ 248.084073] __vfs_write+0x48/0x138 > [ 248.088113] vfs_write+0xa8/0x1b8 > [ 248.091983] SyS_write+0x54/0xb0 > [ 248.095768] el0_svc_naked+0x24/0x28 > [ 248.099897] > [ 248.099897] -> #0 (&u->msgbuffer_mutex){+.+.+.}: > [ 248.106088] print_circular_bug+0x80/0x2e0 > [ 248.110730] __lock_acquire+0x1768/0x1778 > [ 248.115288] lock_acquire+0xc4/0x288 > [ 248.119417] __mutex_lock+0x84/0x868 > [ 248.123545] mutex_lock_nested+0x3c/0x50 > [ 248.128016] xenbus_dev_queue_reply+0x3c/0x230 > [ 248.133005] xenbus_thread+0x788/0x798 > [ 248.137306] kthread+0x110/0x140 > [ 248.141087] ret_from_fork+0x10/0x40 > > It is rather easy to avoid by dropping xb_write_mutex before calling > xenbus_dev_queue_reply(). > > Fixes fd8aa9095a95c02dcc35540a263267c29b8fda9d ("xen: optimize xenbus > driver for multiple concurrent xenstore accesses"). > > Cc: <stable@vger.kernel.org> # 4.11 > Reported-by: Andre Przywara <andre.przywara@arm.com> > Signed-off-by: Juergen Gross <jgross@suse.com> While this patch is functionally okay, the resulting code is not very nice. Will send out V2 soon looking much better. Juergen > --- > drivers/xen/xenbus/xenbus_comms.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c > index 856ada5d39c9..a44bcdbf6533 100644 > --- a/drivers/xen/xenbus/xenbus_comms.c > +++ b/drivers/xen/xenbus/xenbus_comms.c > @@ -305,18 +305,21 @@ static int process_msg(void) > req->body = state.body; > req->state = xb_req_state_got_reply; > list_del(&req->list); > + mutex_unlock(&xb_write_mutex); > req->cb(req); > } else { > list_del(&req->list); > + mutex_unlock(&xb_write_mutex); > kfree(req); > } > err = 0; > break; > } > } > - mutex_unlock(&xb_write_mutex); > - if (err) > + if (err) { > + mutex_unlock(&xb_write_mutex); > goto out; > + } > } > > mutex_unlock(&xs_response_mutex); >
Hi Jürgen, On 08/06/17 15:00, Juergen Gross wrote: > On 07/06/17 18:24, Juergen Gross wrote: >> There has been a report about a deadlock in the xenbus driver: >> >> [ 247.979498] ====================================================== >> [ 247.985688] WARNING: possible circular locking dependency detected >> [ 247.991882] 4.12.0-rc4-00022-gc4b25c0 #575 Not tainted >> [ 247.997040] ------------------------------------------------------ >> [ 248.003232] xenbus/91 is trying to acquire lock: >> [ 248.007875] (&u->msgbuffer_mutex){+.+.+.}, at: [<ffff00000863e904>] >> xenbus_dev_queue_reply+0x3c/0x230 >> [ 248.017163] >> [ 248.017163] but task is already holding lock: >> [ 248.023096] (xb_write_mutex){+.+...}, at: [<ffff00000863a940>] >> xenbus_thread+0x5f0/0x798 >> [ 248.031267] >> [ 248.031267] which lock already depends on the new lock. >> [ 248.031267] >> [ 248.039615] >> [ 248.039615] the existing dependency chain (in reverse order) is: >> [ 248.047176] >> [ 248.047176] -> #1 (xb_write_mutex){+.+...}: >> [ 248.052943] __lock_acquire+0x1728/0x1778 >> [ 248.057498] lock_acquire+0xc4/0x288 >> [ 248.061630] __mutex_lock+0x84/0x868 >> [ 248.065755] mutex_lock_nested+0x3c/0x50 >> [ 248.070227] xs_send+0x164/0x1f8 >> [ 248.074015] xenbus_dev_request_and_reply+0x6c/0x88 >> [ 248.079427] xenbus_file_write+0x260/0x420 >> [ 248.084073] __vfs_write+0x48/0x138 >> [ 248.088113] vfs_write+0xa8/0x1b8 >> [ 248.091983] SyS_write+0x54/0xb0 >> [ 248.095768] el0_svc_naked+0x24/0x28 >> [ 248.099897] >> [ 248.099897] -> #0 (&u->msgbuffer_mutex){+.+.+.}: >> [ 248.106088] print_circular_bug+0x80/0x2e0 >> [ 248.110730] __lock_acquire+0x1768/0x1778 >> [ 248.115288] lock_acquire+0xc4/0x288 >> [ 248.119417] __mutex_lock+0x84/0x868 >> [ 248.123545] mutex_lock_nested+0x3c/0x50 >> [ 248.128016] xenbus_dev_queue_reply+0x3c/0x230 >> [ 248.133005] xenbus_thread+0x788/0x798 >> [ 248.137306] kthread+0x110/0x140 >> [ 248.141087] ret_from_fork+0x10/0x40 >> >> It is rather easy to avoid by dropping xb_write_mutex before calling >> xenbus_dev_queue_reply(). >> >> Fixes fd8aa9095a95c02dcc35540a263267c29b8fda9d ("xen: optimize xenbus >> driver for multiple concurrent xenstore accesses"). >> >> Cc: <stable@vger.kernel.org> # 4.11 >> Reported-by: Andre Przywara <andre.przywara@arm.com> >> Signed-off-by: Juergen Gross <jgross@suse.com> > > While this patch is functionally okay, the resulting code is not > very nice. Will send out V2 soon looking much better. Thanks anyway for the quick reaction! I will try tomorrow if I can reproduce the old problem and then confirm that the patch fixes it. I think I saw xencommons fail somehow (wrong xen-tools version or using /bin/sh), then fixed that, retried and saw the splat. Cheers, Andre. > Juergen > >> --- >> drivers/xen/xenbus/xenbus_comms.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c >> index 856ada5d39c9..a44bcdbf6533 100644 >> --- a/drivers/xen/xenbus/xenbus_comms.c >> +++ b/drivers/xen/xenbus/xenbus_comms.c >> @@ -305,18 +305,21 @@ static int process_msg(void) >> req->body = state.body; >> req->state = xb_req_state_got_reply; >> list_del(&req->list); >> + mutex_unlock(&xb_write_mutex); >> req->cb(req); >> } else { >> list_del(&req->list); >> + mutex_unlock(&xb_write_mutex); >> kfree(req); >> } >> err = 0; >> break; >> } >> } >> - mutex_unlock(&xb_write_mutex); >> - if (err) >> + if (err) { >> + mutex_unlock(&xb_write_mutex); >> goto out; >> + } >> } >> >> mutex_unlock(&xs_response_mutex); >> >
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c index 856ada5d39c9..a44bcdbf6533 100644 --- a/drivers/xen/xenbus/xenbus_comms.c +++ b/drivers/xen/xenbus/xenbus_comms.c @@ -305,18 +305,21 @@ static int process_msg(void) req->body = state.body; req->state = xb_req_state_got_reply; list_del(&req->list); + mutex_unlock(&xb_write_mutex); req->cb(req); } else { list_del(&req->list); + mutex_unlock(&xb_write_mutex); kfree(req); } err = 0; break; } } - mutex_unlock(&xb_write_mutex); - if (err) + if (err) { + mutex_unlock(&xb_write_mutex); goto out; + } } mutex_unlock(&xs_response_mutex);
There has been a report about a deadlock in the xenbus driver: [ 247.979498] ====================================================== [ 247.985688] WARNING: possible circular locking dependency detected [ 247.991882] 4.12.0-rc4-00022-gc4b25c0 #575 Not tainted [ 247.997040] ------------------------------------------------------ [ 248.003232] xenbus/91 is trying to acquire lock: [ 248.007875] (&u->msgbuffer_mutex){+.+.+.}, at: [<ffff00000863e904>] xenbus_dev_queue_reply+0x3c/0x230 [ 248.017163] [ 248.017163] but task is already holding lock: [ 248.023096] (xb_write_mutex){+.+...}, at: [<ffff00000863a940>] xenbus_thread+0x5f0/0x798 [ 248.031267] [ 248.031267] which lock already depends on the new lock. [ 248.031267] [ 248.039615] [ 248.039615] the existing dependency chain (in reverse order) is: [ 248.047176] [ 248.047176] -> #1 (xb_write_mutex){+.+...}: [ 248.052943] __lock_acquire+0x1728/0x1778 [ 248.057498] lock_acquire+0xc4/0x288 [ 248.061630] __mutex_lock+0x84/0x868 [ 248.065755] mutex_lock_nested+0x3c/0x50 [ 248.070227] xs_send+0x164/0x1f8 [ 248.074015] xenbus_dev_request_and_reply+0x6c/0x88 [ 248.079427] xenbus_file_write+0x260/0x420 [ 248.084073] __vfs_write+0x48/0x138 [ 248.088113] vfs_write+0xa8/0x1b8 [ 248.091983] SyS_write+0x54/0xb0 [ 248.095768] el0_svc_naked+0x24/0x28 [ 248.099897] [ 248.099897] -> #0 (&u->msgbuffer_mutex){+.+.+.}: [ 248.106088] print_circular_bug+0x80/0x2e0 [ 248.110730] __lock_acquire+0x1768/0x1778 [ 248.115288] lock_acquire+0xc4/0x288 [ 248.119417] __mutex_lock+0x84/0x868 [ 248.123545] mutex_lock_nested+0x3c/0x50 [ 248.128016] xenbus_dev_queue_reply+0x3c/0x230 [ 248.133005] xenbus_thread+0x788/0x798 [ 248.137306] kthread+0x110/0x140 [ 248.141087] ret_from_fork+0x10/0x40 It is rather easy to avoid by dropping xb_write_mutex before calling xenbus_dev_queue_reply(). Fixes fd8aa9095a95c02dcc35540a263267c29b8fda9d ("xen: optimize xenbus driver for multiple concurrent xenstore accesses"). Cc: <stable@vger.kernel.org> # 4.11 Reported-by: Andre Przywara <andre.przywara@arm.com> Signed-off-by: Juergen Gross <jgross@suse.com> --- drivers/xen/xenbus/xenbus_comms.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)