Messages in this thread |  | | Subject | Re: [PATCH] f2fs: Fix direct IO handling | From | Chao Yu <> | Date | Sat, 30 Nov 2019 15:27:29 +0800 |
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On 2019/11/28 18:20, Ritesh Harjani wrote: > > > On 11/28/19 7:40 AM, Damien Le Moal wrote: >> On 2019/11/26 17:34, Ritesh Harjani wrote: >>> Hello Damien, >>> >>> IIUC, you are trying to fix a stale data read by DIO read for the case >>> you explained in your patch w.r.t. DIO-write forced to write as buffIO. >>> >>> Coincidentally I was just looking at the same code path just now. >>> So I do have a query to you/f2fs group. Below could be silly one, as I >>> don't understand F2FS in great detail. >>> >>> How is the stale data by DIO read, is protected against a mmap >>> writes via f2fs_vm_page_mkwrite? >>> >>> f2fs_vm_page_mkwrite() f2fs_direct_IO (read) >>> filemap_write_and_wait_range() >>> -> f2fs_get_blocks() >>> -> submit_bio() >>> >>> -> set_page_dirty() >>> >>> Is above race possible with current f2fs code? >>> i.e. f2fs_direct_IO could read the stale data from the blocks >>> which were allocated due to mmap fault? >> >> The faulted page is locked until the fault is fully processed so direct >> IO has to wait for that to complete first. > > How about below parallelism? > > f2fs_vm_page_mkwrite() f2fs_direct_IO (read) > filemap_write_and_wait_range() > -> down_read(->i_mmap_sem); > -> lock_page() > -> f2fs_get_blocks() > -> submit_bio() > > -> set_page_dirty() > > Can above DIO read not expose the stale data from block which was > allocated in f2fs_vm_page_mkwrite path?
The race can happen, however I doubt the race condition is more complicated as I described in previous reply of mine, could you check that?
Thanks,
> > >> >>> >>> Am I missing something here? >>> >>> -ritesh >>> >>> On 11/26/19 1:27 PM, Damien Le Moal wrote: >>>> f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT >>>> flag for a kiocb structure. However, the file system direct IO handler >>>> function f2fs_direct_IO() may have decided that a direct IO has to be >>>> exececuted as a buffered IO using the function f2fs_force_buffered_io(). >>>> This is the case for instance for volumes including zoned block device >>>> and for unaligned write IOs with LFS mode enabled. >>>> >>>> These 2 different methods of identifying direct IOs can result in >>>> inconsistencies generating stale data access for direct reads after a >>>> direct IO write that is treated as a buffered write. Fix this >>>> inconsistency by combining the IOCB_DIRECT flag test with the result >>>> of f2fs_force_buffered_io(). >>>> >>>> Reported-by: Javier Gonzalez <javier@javigon.com> >>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> >>>> --- >>>> fs/f2fs/data.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >>>> index 5755e897a5f0..8ac2d3b70022 100644 >>>> --- a/fs/f2fs/data.c >>>> +++ b/fs/f2fs/data.c >>>> @@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >>>> int flag; >>>> int err = 0; >>>> bool direct_io = iocb->ki_flags & IOCB_DIRECT; >>>> + bool do_direct_io = direct_io && >>>> + !f2fs_force_buffered_io(inode, iocb, from); >>>> >>>> /* convert inline data for Direct I/O*/ >>>> if (direct_io) { >>>> @@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from) >>>> return err; >>>> } >>>> >>>> - if (direct_io && allow_outplace_dio(inode, iocb, from)) >>>> + if (do_direct_io && allow_outplace_dio(inode, iocb, from)) >>>> return 0; >>>> >>>> if (is_inode_flag_set(inode, FI_NO_PREALLOC)) >>>> >>> >>> >> >> > > . >
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