* bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update"
@ 2020-03-16 12:14 Xiaoguang Wang
2020-03-16 15:24 ` Jens Axboe
2020-03-16 15:46 ` Xiaoguang Wang
0 siblings, 2 replies; 5+ messages in thread
From: Xiaoguang Wang @ 2020-03-16 12:14 UTC (permalink / raw)
To: io-uring; +Cc: [email protected], joseph qi
hi,
While diving into iouring file register/unregister/update codes, seems that
there is one bug in __io_sqe_files_update():
if (ref_switch)
percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
The initial fixed_file_data's refs is 1, assume there are no requests
to get/put this refs, and we firstly register 10 files and later update
these 10 files, and no memory allocations fails, then above two line of
codes in __io_sqe_files_update() will be called, before entering
percpu_ref_switch_to_atomic(), the count of refs is still one, and
|--> percpu_ref_switch_to_atomic
|----> __percpu_ref_switch_mode
|------> __percpu_ref_switch_to_atomic
|-------- > percpu_ref_get(ref), # now the count of refs will be 2.
a while later
|--> percpu_ref_switch_to_atomic_rcu
|----> percpu_ref_call_confirm_rcu
|------ > confirm_switch(), # calls io_atomic_switch, note that the count of refs is 2.
|------ > percpu_ref_put # drop one ref
static void io_atomic_switch(struct percpu_ref *ref)
{
struct fixed_file_data *data;
/*
* Juggle reference to ensure we hit zero, if needed, so we can
* switch back to percpu mode
*/
data = container_of(ref, struct fixed_file_data, refs);
percpu_ref_put(&data->refs);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
After this operation, the count of refs is 1 now, still not zero, so
io_file_data_ref_zero won't be called, then io_ring_file_ref_flush()
won't be called, this fixed_file_data's refs will always be in atomic mode,
which is bad.
percpu_ref_get(&data->refs);
}
To confirm this bug, I did a hack to kernel:
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5812,7 +5812,10 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
* If we fail allocating the struct we need for doing async reomval
* of this file, just punt to sync and wait for it.
*/
+ /*
pfile = kzalloc(sizeof(*pfile), GFP_KERNEL);
+ */
+ pfile = NULL;
if (!pfile) {
pfile = &pfile_stack;
pfile->done = &done;
To simulate memory allocation failures, then run liburing/test/file-update,
[lege@localhost test]$ sudo cat /proc/2091/stack
[sudo] password for lege:
[<0>] __io_sqe_files_update.isra.85+0x175/0x330
[<0>] __io_uring_register+0x178/0xe20
[<0>] __x64_sys_io_uring_register+0xa0/0x160
[<0>] do_syscall_64+0x55/0x1b0
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
(gdb) list * __io_sqe_files_update+0x175
0xffffffff812ec255 is in __io_sqe_files_update (fs/io_uring.c:5830).
5825 llist_add(&pfile->llist, &data->put_llist);
5826
5827 if (pfile == &pfile_stack) {
5828 percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
5829 wait_for_completion(&done);
5830 flush_work(&data->ref_work);
5831 return false;
file-update will always hang in wait_for_completion(&done), it's because
io_ring_file_ref_flush never has a chance to run.
I think how to fix this issue a while, doesn't find a elegant method yet.
And applications may issue requests continuously, then fixed_file_data's refs
may never have a chance to reach zero, refs will always be in atomic mode.
Or the simplest method is to use percpu_ref per registered file :)
Regards,
Xiaoguang Wang
Regards,
Xiaoguang Wang
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update"
2020-03-16 12:14 bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update" Xiaoguang Wang
@ 2020-03-16 15:24 ` Jens Axboe
2020-03-17 12:13 ` Xiaoguang Wang
2020-03-16 15:46 ` Xiaoguang Wang
1 sibling, 1 reply; 5+ messages in thread
From: Jens Axboe @ 2020-03-16 15:24 UTC (permalink / raw)
To: Xiaoguang Wang, io-uring; +Cc: joseph qi
On 3/16/20 6:14 AM, Xiaoguang Wang wrote:
> hi,
>
> While diving into iouring file register/unregister/update codes, seems that
> there is one bug in __io_sqe_files_update():
> if (ref_switch)
> percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>
> The initial fixed_file_data's refs is 1, assume there are no requests
> to get/put this refs, and we firstly register 10 files and later update
> these 10 files, and no memory allocations fails, then above two line of
> codes in __io_sqe_files_update() will be called, before entering
> percpu_ref_switch_to_atomic(), the count of refs is still one, and
> |--> percpu_ref_switch_to_atomic
> |----> __percpu_ref_switch_mode
> |------> __percpu_ref_switch_to_atomic
> |-------- > percpu_ref_get(ref), # now the count of refs will be 2.
>
> a while later
> |--> percpu_ref_switch_to_atomic_rcu
> |----> percpu_ref_call_confirm_rcu
> |------ > confirm_switch(), # calls io_atomic_switch, note that the count of refs is 2.
> |------ > percpu_ref_put # drop one ref
>
> static void io_atomic_switch(struct percpu_ref *ref)
> {
> struct fixed_file_data *data;
>
> /*
> * Juggle reference to ensure we hit zero, if needed, so we can
> * switch back to percpu mode
> */
> data = container_of(ref, struct fixed_file_data, refs);
> percpu_ref_put(&data->refs);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> After this operation, the count of refs is 1 now, still not zero, so
> io_file_data_ref_zero won't be called, then io_ring_file_ref_flush()
> won't be called, this fixed_file_data's refs will always be in atomic mode,
> which is bad.
>
> percpu_ref_get(&data->refs);
> }
>
> To confirm this bug, I did a hack to kernel:
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5812,7 +5812,10 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
> * If we fail allocating the struct we need for doing async reomval
> * of this file, just punt to sync and wait for it.
> */
> + /*
> pfile = kzalloc(sizeof(*pfile), GFP_KERNEL);
> + */
> + pfile = NULL;
> if (!pfile) {
> pfile = &pfile_stack;
> pfile->done = &done;
> To simulate memory allocation failures, then run liburing/test/file-update,
>
> [lege@localhost test]$ sudo cat /proc/2091/stack
> [sudo] password for lege:
> [<0>] __io_sqe_files_update.isra.85+0x175/0x330
> [<0>] __io_uring_register+0x178/0xe20
> [<0>] __x64_sys_io_uring_register+0xa0/0x160
> [<0>] do_syscall_64+0x55/0x1b0
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> (gdb) list * __io_sqe_files_update+0x175
> 0xffffffff812ec255 is in __io_sqe_files_update (fs/io_uring.c:5830).
> 5825 llist_add(&pfile->llist, &data->put_llist);
> 5826
> 5827 if (pfile == &pfile_stack) {
> 5828 percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
> 5829 wait_for_completion(&done);
> 5830 flush_work(&data->ref_work);
> 5831 return false;
>
> file-update will always hang in wait_for_completion(&done), it's because
> io_ring_file_ref_flush never has a chance to run.
>
> I think how to fix this issue a while, doesn't find a elegant method yet.
> And applications may issue requests continuously, then fixed_file_data's refs
> may never have a chance to reach zero, refs will always be in atomic mode.
> Or the simplest method is to use percpu_ref per registered file :)
For the "oh crap I can't allocate data" stack path, I think the below
should fix it. Might not be a bad idea to re-think the live updates in
general, though.
diff --git a/fs/io_uring.c b/fs/io_uring.c
index b1fbc4424aa6..3f0c8291a17c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5612,10 +5612,12 @@ static void io_ring_file_ref_flush(struct fixed_file_data *data)
while ((node = llist_del_all(&data->put_llist)) != NULL) {
llist_for_each_entry_safe(pfile, tmp, node, llist) {
io_ring_file_put(data->ctx, pfile->file);
- if (pfile->done)
+ if (pfile->done) {
+ percpu_ref_get(&data->refs);
complete(pfile->done);
- else
+ } else {
kfree(pfile);
+ }
}
}
}
@@ -5830,6 +5836,7 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
llist_add(&pfile->llist, &data->put_llist);
if (pfile == &pfile_stack) {
+ percpu_ref_put(&data->refs);
percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
wait_for_completion(&done);
flush_work(&data->ref_work);
--
Jens Axboe
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update"
2020-03-16 12:14 bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update" Xiaoguang Wang
2020-03-16 15:24 ` Jens Axboe
@ 2020-03-16 15:46 ` Xiaoguang Wang
1 sibling, 0 replies; 5+ messages in thread
From: Xiaoguang Wang @ 2020-03-16 15:46 UTC (permalink / raw)
To: io-uring; +Cc: [email protected], joseph qi
hi,
> hi,
>
> While diving into iouring file register/unregister/update codes, seems that
> there is one bug in __io_sqe_files_update():
> if (ref_switch)
> percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>
> The initial fixed_file_data's refs is 1, assume there are no requests
> to get/put this refs, and we firstly register 10 files and later update
> these 10 files, and no memory allocations fails, then above two line of
> codes in __io_sqe_files_update() will be called, before entering
> percpu_ref_switch_to_atomic(), the count of refs is still one, and
> |--> percpu_ref_switch_to_atomic
> |----> __percpu_ref_switch_mode
> |------> __percpu_ref_switch_to_atomic
> |-------- > percpu_ref_get(ref), # now the count of refs will be 2.
>
> a while later
> |--> percpu_ref_switch_to_atomic_rcu
> |----> percpu_ref_call_confirm_rcu
> |------ > confirm_switch(), # calls io_atomic_switch, note that the count of refs is 2.
> |------ > percpu_ref_put # drop one ref
>
> static void io_atomic_switch(struct percpu_ref *ref)
> {
> struct fixed_file_data *data;
>
> /*
> * Juggle reference to ensure we hit zero, if needed, so we can
> * switch back to percpu mode
> */
> data = container_of(ref, struct fixed_file_data, refs);
> percpu_ref_put(&data->refs);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> After this operation, the count of refs is 1 now, still not zero, so
> io_file_data_ref_zero won't be called, then io_ring_file_ref_flush()
> won't be called, this fixed_file_data's refs will always be in atomic mode,
> which is bad.
>
> percpu_ref_get(&data->refs);
> }
Even don't consider below pfile memory allocation failure, because before entering
io_atomic_switch(), the count of refs is 2, the percpu_ref_put calls in io_atomic_switch
makes the count of refs to be 1, so io_file_data_ref_zero still won't be called, and
refs will always be in atomic mode? Normal reqs just add/dec 1 to the refs, so the cout
of refs will never have a chance to reach zero.
What I worry is that when we finish __io_sqe_files_update, whether fixed_file_data's refs
will always be in atomic mode.
Regards,
Xiaoguang Wang
>
> To confirm this bug, I did a hack to kernel:
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5812,7 +5812,10 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
> * If we fail allocating the struct we need for doing async reomval
> * of this file, just punt to sync and wait for it.
> */
> + /*
> pfile = kzalloc(sizeof(*pfile), GFP_KERNEL);
> + */
> + pfile = NULL;
> if (!pfile) {
> pfile = &pfile_stack;
> pfile->done = &done;
> To simulate memory allocation failures, then run liburing/test/file-update,
>
> [lege@localhost test]$ sudo cat /proc/2091/stack
> [sudo] password for lege:
> [<0>] __io_sqe_files_update.isra.85+0x175/0x330
> [<0>] __io_uring_register+0x178/0xe20
> [<0>] __x64_sys_io_uring_register+0xa0/0x160
> [<0>] do_syscall_64+0x55/0x1b0
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> (gdb) list * __io_sqe_files_update+0x175
> 0xffffffff812ec255 is in __io_sqe_files_update (fs/io_uring.c:5830).
> 5825 llist_add(&pfile->llist, &data->put_llist);
> 5826
> 5827 if (pfile == &pfile_stack) {
> 5828 percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
> 5829 wait_for_completion(&done);
> 5830 flush_work(&data->ref_work);
> 5831 return false;
>
> file-update will always hang in wait_for_completion(&done), it's because
> io_ring_file_ref_flush never has a chance to run.
>
> I think how to fix this issue a while, doesn't find a elegant method yet.
> And applications may issue requests continuously, then fixed_file_data's refs
> may never have a chance to reach zero, refs will always be in atomic mode.
> Or the simplest method is to use percpu_ref per registered file :)
>
> Regards,
> Xiaoguang Wang
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> Regards,
> Xiaoguang Wang
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update"
2020-03-16 15:24 ` Jens Axboe
@ 2020-03-17 12:13 ` Xiaoguang Wang
2020-03-17 14:38 ` Jens Axboe
0 siblings, 1 reply; 5+ messages in thread
From: Xiaoguang Wang @ 2020-03-17 12:13 UTC (permalink / raw)
To: Jens Axboe, io-uring; +Cc: joseph qi
hi,
> On 3/16/20 6:14 AM, Xiaoguang Wang wrote:
>> hi,
>>
>> While diving into iouring file register/unregister/update codes, seems that
>> there is one bug in __io_sqe_files_update():
>> if (ref_switch)
>> percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>>
>> The initial fixed_file_data's refs is 1, assume there are no requests
>> to get/put this refs, and we firstly register 10 files and later update
>> these 10 files, and no memory allocations fails, then above two line of
>> codes in __io_sqe_files_update() will be called, before entering
>> percpu_ref_switch_to_atomic(), the count of refs is still one, and
>> |--> percpu_ref_switch_to_atomic
>> |----> __percpu_ref_switch_mode
>> |------> __percpu_ref_switch_to_atomic
>> |-------- > percpu_ref_get(ref), # now the count of refs will be 2.
>>
>> a while later
>> |--> percpu_ref_switch_to_atomic_rcu
>> |----> percpu_ref_call_confirm_rcu
>> |------ > confirm_switch(), # calls io_atomic_switch, note that the count of refs is 2.
>> |------ > percpu_ref_put # drop one ref
>>
>> static void io_atomic_switch(struct percpu_ref *ref)
>> {
>> struct fixed_file_data *data;
>>
>> /*
>> * Juggle reference to ensure we hit zero, if needed, so we can
>> * switch back to percpu mode
>> */
>> data = container_of(ref, struct fixed_file_data, refs);
>> percpu_ref_put(&data->refs);
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> After this operation, the count of refs is 1 now, still not zero, so
>> io_file_data_ref_zero won't be called, then io_ring_file_ref_flush()
>> won't be called, this fixed_file_data's refs will always be in atomic mode,
>> which is bad.
>>
>> percpu_ref_get(&data->refs);
>> }
>>
>> To confirm this bug, I did a hack to kernel:
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -5812,7 +5812,10 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
>> * If we fail allocating the struct we need for doing async reomval
>> * of this file, just punt to sync and wait for it.
>> */
>> + /*
>> pfile = kzalloc(sizeof(*pfile), GFP_KERNEL);
>> + */
>> + pfile = NULL;
>> if (!pfile) {
>> pfile = &pfile_stack;
>> pfile->done = &done;
>> To simulate memory allocation failures, then run liburing/test/file-update,
>>
>> [lege@localhost test]$ sudo cat /proc/2091/stack
>> [sudo] password for lege:
>> [<0>] __io_sqe_files_update.isra.85+0x175/0x330
>> [<0>] __io_uring_register+0x178/0xe20
>> [<0>] __x64_sys_io_uring_register+0xa0/0x160
>> [<0>] do_syscall_64+0x55/0x1b0
>> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> (gdb) list * __io_sqe_files_update+0x175
>> 0xffffffff812ec255 is in __io_sqe_files_update (fs/io_uring.c:5830).
>> 5825 llist_add(&pfile->llist, &data->put_llist);
>> 5826
>> 5827 if (pfile == &pfile_stack) {
>> 5828 percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>> 5829 wait_for_completion(&done);
>> 5830 flush_work(&data->ref_work);
>> 5831 return false;
>>
>> file-update will always hang in wait_for_completion(&done), it's because
>> io_ring_file_ref_flush never has a chance to run.
>>
>> I think how to fix this issue a while, doesn't find a elegant method yet.
>> And applications may issue requests continuously, then fixed_file_data's refs
>> may never have a chance to reach zero, refs will always be in atomic mode.
>> Or the simplest method is to use percpu_ref per registered file :)
>
> For the "oh crap I can't allocate data" stack path, I think the below
> should fix it. Might not be a bad idea to re-think the live updates in
> general, though.
I'm not a native english speaker and afraid that I may misread your replies :)
So I'd like to confirm that do you mind that I implement a percpu_ref per
registered file to track every registered file's status?
Regards,
Xiaoguang Wang
>
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b1fbc4424aa6..3f0c8291a17c 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5612,10 +5612,12 @@ static void io_ring_file_ref_flush(struct fixed_file_data *data)
> while ((node = llist_del_all(&data->put_llist)) != NULL) {
> llist_for_each_entry_safe(pfile, tmp, node, llist) {
> io_ring_file_put(data->ctx, pfile->file);
> - if (pfile->done)
> + if (pfile->done) {
> + percpu_ref_get(&data->refs);
> complete(pfile->done);
> - else
> + } else {
> kfree(pfile);
> + }
> }
> }
> }
> @@ -5830,6 +5836,7 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
> llist_add(&pfile->llist, &data->put_llist);
>
> if (pfile == &pfile_stack) {
> + percpu_ref_put(&data->refs);
> percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
> wait_for_completion(&done);
> flush_work(&data->ref_work);
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update"
2020-03-17 12:13 ` Xiaoguang Wang
@ 2020-03-17 14:38 ` Jens Axboe
0 siblings, 0 replies; 5+ messages in thread
From: Jens Axboe @ 2020-03-17 14:38 UTC (permalink / raw)
To: Xiaoguang Wang, io-uring; +Cc: joseph qi
On 3/17/20 6:13 AM, Xiaoguang Wang wrote:
> hi,
>
>> On 3/16/20 6:14 AM, Xiaoguang Wang wrote:
>>> hi,
>>>
>>> While diving into iouring file register/unregister/update codes, seems that
>>> there is one bug in __io_sqe_files_update():
>>> if (ref_switch)
>>> percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>>>
>>> The initial fixed_file_data's refs is 1, assume there are no requests
>>> to get/put this refs, and we firstly register 10 files and later update
>>> these 10 files, and no memory allocations fails, then above two line of
>>> codes in __io_sqe_files_update() will be called, before entering
>>> percpu_ref_switch_to_atomic(), the count of refs is still one, and
>>> |--> percpu_ref_switch_to_atomic
>>> |----> __percpu_ref_switch_mode
>>> |------> __percpu_ref_switch_to_atomic
>>> |-------- > percpu_ref_get(ref), # now the count of refs will be 2.
>>>
>>> a while later
>>> |--> percpu_ref_switch_to_atomic_rcu
>>> |----> percpu_ref_call_confirm_rcu
>>> |------ > confirm_switch(), # calls io_atomic_switch, note that the count of refs is 2.
>>> |------ > percpu_ref_put # drop one ref
>>>
>>> static void io_atomic_switch(struct percpu_ref *ref)
>>> {
>>> struct fixed_file_data *data;
>>>
>>> /*
>>> * Juggle reference to ensure we hit zero, if needed, so we can
>>> * switch back to percpu mode
>>> */
>>> data = container_of(ref, struct fixed_file_data, refs);
>>> percpu_ref_put(&data->refs);
>>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> After this operation, the count of refs is 1 now, still not zero, so
>>> io_file_data_ref_zero won't be called, then io_ring_file_ref_flush()
>>> won't be called, this fixed_file_data's refs will always be in atomic mode,
>>> which is bad.
>>>
>>> percpu_ref_get(&data->refs);
>>> }
>>>
>>> To confirm this bug, I did a hack to kernel:
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -5812,7 +5812,10 @@ static bool io_queue_file_removal(struct fixed_file_data *data,
>>> * If we fail allocating the struct we need for doing async reomval
>>> * of this file, just punt to sync and wait for it.
>>> */
>>> + /*
>>> pfile = kzalloc(sizeof(*pfile), GFP_KERNEL);
>>> + */
>>> + pfile = NULL;
>>> if (!pfile) {
>>> pfile = &pfile_stack;
>>> pfile->done = &done;
>>> To simulate memory allocation failures, then run liburing/test/file-update,
>>>
>>> [lege@localhost test]$ sudo cat /proc/2091/stack
>>> [sudo] password for lege:
>>> [<0>] __io_sqe_files_update.isra.85+0x175/0x330
>>> [<0>] __io_uring_register+0x178/0xe20
>>> [<0>] __x64_sys_io_uring_register+0xa0/0x160
>>> [<0>] do_syscall_64+0x55/0x1b0
>>> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>> (gdb) list * __io_sqe_files_update+0x175
>>> 0xffffffff812ec255 is in __io_sqe_files_update (fs/io_uring.c:5830).
>>> 5825 llist_add(&pfile->llist, &data->put_llist);
>>> 5826
>>> 5827 if (pfile == &pfile_stack) {
>>> 5828 percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch);
>>> 5829 wait_for_completion(&done);
>>> 5830 flush_work(&data->ref_work);
>>> 5831 return false;
>>>
>>> file-update will always hang in wait_for_completion(&done), it's because
>>> io_ring_file_ref_flush never has a chance to run.
>>>
>>> I think how to fix this issue a while, doesn't find a elegant method yet.
>>> And applications may issue requests continuously, then fixed_file_data's refs
>>> may never have a chance to reach zero, refs will always be in atomic mode.
>>> Or the simplest method is to use percpu_ref per registered file :)
>>
>> For the "oh crap I can't allocate data" stack path, I think the below
>> should fix it. Might not be a bad idea to re-think the live updates in
>> general, though.
>
> I'm not a native english speaker and afraid that I may misread your
> replies :) So I'd like to confirm that do you mind that I implement a
> percpu_ref per registered file to track every registered file's
> status?
That'd be great, as long as we're ensuring that memory bloat doesn't
become a problem. But never doubt that you can send patches to improve
things - even if they sometimes don't get applied, they may help spark
discussion that will end up leading to a great fix.
--
Jens Axboe
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-03-17 14:38 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2020-03-16 12:14 bug report about patch "io_uring: avoid ring quiesce for fixed file set unregister and update" Xiaoguang Wang
2020-03-16 15:24 ` Jens Axboe
2020-03-17 12:13 ` Xiaoguang Wang
2020-03-17 14:38 ` Jens Axboe
2020-03-16 15:46 ` Xiaoguang Wang
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