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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 17:33:50 +0000 |
29.03.2019 20:30, Max Reitz wrote:
> 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 .
>
raw_apply_lock_bytes failes in my cases. And it is because it calls fcntl to
lock bytes
even on loosening.
--
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 <=
- 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, 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