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    SubjectRe: [PATCH] ext3_getblk should handle HOLE correctly
    On Thu, 07 Sep 2006 12:22:27 -0700
    Badari Pulavarty <pbadari@us.ibm.com> wrote:

    > On Thu, 2006-09-07 at 11:45 -0700, Andrew Morton wrote:
    > > On Wed, 06 Sep 2006 10:39:06 -0700
    > > Badari Pulavarty <pbadari@us.ibm.com> wrote:
    > >
    > > > Hi Andrew,
    > > >
    > > > Its been reported that ext3_getblk() is not doing the right thing
    > > > and triggering following WARN():
    > > >
    > > > BUG: warning at fs/ext3/inode.c:1016/ext3_getblk()
    > > > <c01c5140> ext3_getblk+0x98/0x2a6 <c03b2806> md_wakeup_thread
    > > > +0x26/0x2a
    > > > <c01c536d> ext3_bread+0x1f/0x88 <c01cedf9> ext3_quota_read+0x136/0x1ae
    > > > <c018b683> v1_read_dqblk+0x61/0xac <c0188f32> dquot_acquire+0xf6/0x107
    > > > <c01ceaba> ext3_acquire_dquot+0x46/0x68 <c01897d4> dqget+0x155/0x1e7
    > > > <c018a97b> dquot_transfer+0x3e0/0x3e9 <c016fe52> dput+0x23/0x13e
    > > > <c01c7986> ext3_setattr+0xc3/0x240 <c0120f66> current_fs_time
    > > > +0x52/0x6a
    > > > <c017320e> notify_change+0x2bd/0x30d <c0159246> chown_common+0x9c/0xc5
    > > > <c02a222c> strncpy_from_user+0x3b/0x68 <c0167fe6> do_path_lookup
    > > > +0xdf/0x266
    > > > <c016841b> __user_walk_fd+0x44/0x5a <c01592b9> sys_chown+0x4a/0x55
    > > > <c015a43c> vfs_write+0xe7/0x13c <c01695d4> sys_mkdir+0x1f/0x23
    > > > <c0102a97> syscall_call+0x7/0xb
    > > >
    > > > Looking at the code, it looks like its not handle HOLE correctly.
    > > > It ends up returning -EIO.
    > >
    > > Strange. The fs should be spewing these warnings all over the place. For
    > > some reason this code is hard to trigger. Why??
    >
    > I guess - ext3_getblk() mostly used by ext3_bread() and most callers
    > to it would be reading already allocated block.

    OK.

    > >
    > > > - if (err == 1) {
    > > > + /*
    > > > + * ext3_get_blocks_handle() returns number of blocks
    > > > + * mapped. 0 in case of a HOLE.
    > > > + */
    > > > + if (err > 0) {
    > > > err = 0;
    > > > - } else if (err >= 0) {
    > > > - WARN_ON(1);
    > > > - err = -EIO;
    > > > }
    > >
    > > That removes the warning if ext3_get_blocks_handle() returned a positive
    > > number greater than one. And it looks like we still need debugging support
    > > in this area.
    >
    > I am not sure why we need it ? All we care about is one block. If
    > ext3_get_blocks_handle() returns more than one (which it shouldn't) -

    The operative part is "which it shouldn't". This code is fairly fresh, and
    ext3 is paranoid. Once it's all settled down then after a year or so we
    might decide that the debugging code is no longer needed.

    Then again, we have plenty of five-year-old assertions in there..

    -
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