| Message ID | 1463156728-13357-1-git-send-email-guaneryu@gmail.com |
|---|---|
| State | New, archived |
| Headers | show |
Eryu Guan <guaneryu@gmail.com> writes: > What we should really do is to disable block allocation for writes that > could result in filling holes inside i_size. > > Reviewed-by: Jan Kara <jack@suse.cz> > Signed-off-by: Eryu Guan <guaneryu@gmail.com> This looks good to me, Eryu, and it passes the aio/dio test cases in xfstests and libaio. Thanks a lot! Al, can you take this through your tree? Reviewed-by: Jeff Moyer <jmoyer@redhat.com> > --- > > v3: > - Kill unnecessary cleanup patch > - Update comments a bit accordingly > > v2: > - Fix the case Jeff pointed out as well > - Update commit log > > fs/direct-io.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/fs/direct-io.c b/fs/direct-io.c > index 4720377..62921ce 100644 > --- a/fs/direct-io.c > +++ b/fs/direct-io.c > @@ -627,11 +627,11 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, > map_bh->b_size = fs_count << i_blkbits; > > /* > - * For writes inside i_size on a DIO_SKIP_HOLES filesystem we > - * forbid block creations: only overwrites are permitted. > - * We will return early to the caller once we see an > - * unmapped buffer head returned, and the caller will fall > - * back to buffered I/O. > + * For writes that could fill holes inside i_size on a > + * DIO_SKIP_HOLES filesystem we forbid block creations: only > + * overwrites are permitted. We will return early to the caller > + * once we see an unmapped buffer head returned, and the caller > + * will fall back to buffered I/O. > * > * Otherwise the decision is left to the get_blocks method, > * which may decide to handle it or also return an unmapped > @@ -639,8 +639,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, > */ > create = dio->rw & WRITE; > if (dio->flags & DIO_SKIP_HOLES) { > - if (sdio->block_in_file < (i_size_read(dio->inode) >> > - sdio->blkbits)) > + if (fs_startblk <= ((i_size_read(dio->inode) - 1) >> > + i_blkbits)) > create = 0; > } -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Jeff Moyer <jmoyer@redhat.com> writes: > Eryu Guan <guaneryu@gmail.com> writes: > >> What we should really do is to disable block allocation for writes that >> could result in filling holes inside i_size. >> >> Reviewed-by: Jan Kara <jack@suse.cz> >> Signed-off-by: Eryu Guan <guaneryu@gmail.com> > > This looks good to me, Eryu, and it passes the aio/dio test cases in > xfstests and libaio. Thanks a lot! > > Al, can you take this through your tree? No response from Al. Andrew, would you mind grabbing this? Thanks, Jeff > Reviewed-by: Jeff Moyer <jmoyer@redhat.com> > > >> --- >> >> v3: >> - Kill unnecessary cleanup patch >> - Update comments a bit accordingly >> >> v2: >> - Fix the case Jeff pointed out as well >> - Update commit log >> >> fs/direct-io.c | 14 +++++++------- >> 1 file changed, 7 insertions(+), 7 deletions(-) >> >> diff --git a/fs/direct-io.c b/fs/direct-io.c >> index 4720377..62921ce 100644 >> --- a/fs/direct-io.c >> +++ b/fs/direct-io.c >> @@ -627,11 +627,11 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, >> map_bh->b_size = fs_count << i_blkbits; >> >> /* >> - * For writes inside i_size on a DIO_SKIP_HOLES filesystem we >> - * forbid block creations: only overwrites are permitted. >> - * We will return early to the caller once we see an >> - * unmapped buffer head returned, and the caller will fall >> - * back to buffered I/O. >> + * For writes that could fill holes inside i_size on a >> + * DIO_SKIP_HOLES filesystem we forbid block creations: only >> + * overwrites are permitted. We will return early to the caller >> + * once we see an unmapped buffer head returned, and the caller >> + * will fall back to buffered I/O. >> * >> * Otherwise the decision is left to the get_blocks method, >> * which may decide to handle it or also return an unmapped >> @@ -639,8 +639,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, >> */ >> create = dio->rw & WRITE; >> if (dio->flags & DIO_SKIP_HOLES) { >> - if (sdio->block_in_file < (i_size_read(dio->inode) >> >> - sdio->blkbits)) >> + if (fs_startblk <= ((i_size_read(dio->inode) - 1) >> >> + i_blkbits)) >> create = 0; >> } > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat, 14 May 2016 00:25:28 +0800 Eryu Guan <guaneryu@gmail.com> wrote: > Currently direct writes inside i_size on a DIO_SKIP_HOLES filesystem are > not allowed to allocate blocks(get_more_blocks() sets 'create' to 0 > before calling get_block() callback), if it's a sparse file, direct > writes fall back to buffered writes to avoid stale data exposure from > concurrent buffered read. But there're two cases that can result in > stale data exposure are not correctly detected. > > 1. The detection for "writing inside i_size" is not sufficient, writes > can be treated as "extending writes" wrongly. For example, direct write > 1FSB to a 1FSB sparse file on ext2/3/4, starting from offset 0, in this > case it's writing inside i_size, but 'create' is non-zero, because > 'block_in_file' and '(i_size_read(inode) >> blkbits' are both zero. um, what is an "FSB"? > 2. Direct writes starting from or beyong i_size (not inside i_size) also > could trigger block allocation and expose stale data. For example, > consider a sparse file with i_size of 2k, and a write to offset 2k or 3k > into the file, with a filesystem block size of 4k. (Thanks to Jeff Moyer > for pointing this case out in his review.) > > The first problem can be demostrated by running ltp-aiodio test ADSP045 > many times. When testing on extN filesystems, I see test failures > occasionally, buffered read could read non-zero (stale) data. > > ADSP045: dio_sparse -a 4k -w 4k -s 2k -n 1 > > dio_sparse 0 TINFO : Dirtying free blocks > dio_sparse 0 TINFO : Starting I/O tests > non zero buffer at buf[0] => 0xffffffaa,ffffffaa,ffffffaa,ffffffaa > non-zero read at offset 0 > dio_sparse 0 TINFO : Killing childrens(s) > dio_sparse 1 TFAIL : dio_sparse.c:191: 1 children(s) exited abnormally > > The second problem can also be reproduced easily by a hacked dio_sparse > program, which accepts an option to specify the write offset. > > What we should really do is to disable block allocation for writes that > could result in filling holes inside i_size. > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Andrew Morton <akpm@linux-foundation.org> writes: > On Sat, 14 May 2016 00:25:28 +0800 Eryu Guan <guaneryu@gmail.com> wrote: > >> Currently direct writes inside i_size on a DIO_SKIP_HOLES filesystem are >> not allowed to allocate blocks(get_more_blocks() sets 'create' to 0 >> before calling get_block() callback), if it's a sparse file, direct >> writes fall back to buffered writes to avoid stale data exposure from >> concurrent buffered read. But there're two cases that can result in >> stale data exposure are not correctly detected. >> >> 1. The detection for "writing inside i_size" is not sufficient, writes >> can be treated as "extending writes" wrongly. For example, direct write >> 1FSB to a 1FSB sparse file on ext2/3/4, starting from offset 0, in this >> case it's writing inside i_size, but 'create' is non-zero, because >> 'block_in_file' and '(i_size_read(inode) >> blkbits' are both zero. > > um, what is an "FSB"? File System Block, as opposed to a block device block. :) -Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/direct-io.c b/fs/direct-io.c index 4720377..62921ce 100644 --- a/fs/direct-io.c +++ b/fs/direct-io.c @@ -627,11 +627,11 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, map_bh->b_size = fs_count << i_blkbits; /* - * For writes inside i_size on a DIO_SKIP_HOLES filesystem we - * forbid block creations: only overwrites are permitted. - * We will return early to the caller once we see an - * unmapped buffer head returned, and the caller will fall - * back to buffered I/O. + * For writes that could fill holes inside i_size on a + * DIO_SKIP_HOLES filesystem we forbid block creations: only + * overwrites are permitted. We will return early to the caller + * once we see an unmapped buffer head returned, and the caller + * will fall back to buffered I/O. * * Otherwise the decision is left to the get_blocks method, * which may decide to handle it or also return an unmapped @@ -639,8 +639,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio, */ create = dio->rw & WRITE; if (dio->flags & DIO_SKIP_HOLES) { - if (sdio->block_in_file < (i_size_read(dio->inode) >> - sdio->blkbits)) + if (fs_startblk <= ((i_size_read(dio->inode) - 1) >> + i_blkbits)) create = 0; }