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Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock byte
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes |
Date: |
Fri, 29 Mar 2019 17:58:59 +0000 |
29.03.2019 20:44, Max Reitz wrote:
> On 29.03.19 18:40, Kevin Wolf wrote:
>> Am 29.03.2019 um 18:30 hat Max Reitz geschrieben:
>>> On 29.03.19 18:24, Kevin Wolf wrote:
>>>> Am 29.03.2019 um 18:15 hat Max Reitz geschrieben:
>>>>> On 29.03.19 12:04, Vladimir Sementsov-Ogievskiy wrote:
>>>>>> bdrv_replace_child() calls bdrv_check_perm() with error_abort on
>>>>>> loosening permissions. However file-locking operations may fail even
>>>>>> in this case, for example on NFS. And this leads to Qemu crash.
>>>>>>
>>>>>> Let's avoid such errors. Note, that we ignore such things anyway on
>>>>>> permission update commit and abort.
>>>>>>
>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>>> ---
>>>>>> block/file-posix.c | 12 ++++++++++++
>>>>>> 1 file changed, 12 insertions(+)
>>>>>>
>>>>>> diff --git a/block/file-posix.c b/block/file-posix.c
>>>>>> index db4cccbe51..1cf4ee49eb 100644
>>>>>> --- a/block/file-posix.c
>>>>>> +++ b/block/file-posix.c
>>>>>> @@ -815,6 +815,18 @@ static int raw_handle_perm_lock(BlockDriverState
>>>>>> *bs,
>>>>>>
>>>>>> switch (op) {
>>>>>> case RAW_PL_PREPARE:
>>>>>> + if ((s->perm | new_perm) == s->perm &&
>>>>>> + (s->shared_perm & new_shared) == s->shared_perm)
>>>>>> + {
>>>>>> + /*
>>>>>> + * We are going to unlock bytes, it should not fail. If it
>>>>>> fail due
>>>>>> + * to some fs-dependent permission-unrelated reasons (which
>>>>>> occurs
>>>>>> + * sometimes on NFS and leads to abort in
>>>>>> bdrv_replace_child) we
>>>>>> + * can't prevent such errors by any check here. And we
>>>>>> ignore them
>>>>>> + * anyway in ABORT and COMMIT.
>>>>>> + */
>>>>>> + return 0;
>>>>>> + }
>>>>>> ret = raw_apply_lock_bytes(s, s->fd, s->perm | new_perm,
>>>>>> ~s->shared_perm | ~new_shared,
>>>>>> false, errp);
>>>>>
>>>>> Help me understand the exact issue, please. I understand that there are
>>>>> operations like bdrv_replace_child() that pass &error_abort to
>>>>> bdrv_check_perm() because they just loosen the permissions, so it should
>>>>> not fail.
>>>>>
>>>>> However, if the whole effect really would be to loosen permissions,
>>>>> raw_apply_lock_bytes() wouldn't have failed here in PREPARE anyway:
>>>>> @unlock is passed as false, so no bytes will be unlocked. And if
>>>>> permissions are just loosened (as your condition checks), it should not
>>>>> lock any bytes.
>>>>>
>>>>> So why does it attempt lock any bytes in the first place? There must be
>>>>> some discrepancy between s->perm and s->locked_perm, or ~s->shared_perm
>>>>> and s->locked_shared_perm. How does that occur?
>>>>
>>>> I suppose raw_check_lock_bytes() is what is failing, not
>>>> raw_apply_lock_bytes().
>>>
>>> Hm, maybe in Vladimir's case, but not in e.g.
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1652572 .
>>
>> This is reported against 3.0, which didn't avoid re-locking permissions
>> that we already hold, so there raw_apply_lock_bytes() can still fail.
>
> That makes sense. Which leaves the question why Vladimir still seems to
> see the error there...?
>
I'm sorry :(. I'm trying to fix bug based on 2.10, and now I see that is
already fixed
upstream. I don't have a reproducer, only old coredumps.
So, now it looks like we don't need this patch, as on permission loosening
file-posix
don't call any FS apis, yes?
--
Best regards,
Vladimir
- [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Vladimir Sementsov-Ogievskiy, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Kevin Wolf, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Max Reitz, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Kevin Wolf, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Max Reitz, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Vladimir Sementsov-Ogievskiy, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Kevin Wolf, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Max Reitz, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes,
Vladimir Sementsov-Ogievskiy <=
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Vladimir Sementsov-Ogievskiy, 2019/03/29
- Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Kevin Wolf, 2019/03/29
Re: [Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes, Vladimir Sementsov-Ogievskiy, 2019/03/29