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    SubjectRe: [PATCH] nfs: Fix nfs_readpages() error path
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    On Mon, 2006-10-30 at 00:56 +0900, OGAWA Hirofumi wrote:
    > I've got the following oops.
    >
    > ------------[ cut here ]------------
    > kernel BUG at /devel/linux/works/linux-2.6/mm/readahead.c:315!
    > invalid opcode: 0000 [#1]
    > SMP
    >
    > [...]
    >
    > EFLAGS: 00210283 (2.6.19-rc3 #3)
    > EIP is at __do_page_cache_readahead+0x1a4/0x1b7
    > eax: f260db64 ebx: f8f9aa18 ecx: 00000001 edx: f7710594
    > esi: f6042b94 edi: f6042b84 ebp: f260db78 esp: f260db0c
    > ds: 007b es: 007b ss: 0068
    > Process emacs (pid: 3694, ti=f260d000 task=f670caa0 task.ti=f260d000)
    > Stack: 00000001 000001ac f25dd88c 0000085e 0000001e 00000001 00001000 d7f4a48c
    > d7f4a50c d7f4a50c 00001000 d7f4a50c f260db60 00200246 00000001 22222222
    > 22222222 d7f4a50c d7f4a50c 00001000 d7f4a48c f260db68 c13cb9f8 c13cb9f8
    > Call Trace:
    > [<c0140a3a>] do_page_cache_readahead+0x43/0x4d
    > [<c013ce9b>] filemap_nopage+0x14e/0x328
    > [<c0145b8e>] __handle_mm_fault+0x146/0x7b6
    > [<c01463cc>] get_user_pages+0x1ce/0x293
    > [<c017f0a8>] elf_core_dump+0xa05/0xba5
    > [<c015b8a7>] do_coredump+0x565/0x5d1
    > [<c0123acb>] get_signal_to_deliver+0x701/0x758
    > [<c010246b>] do_notify_resume+0x8b/0x6c4
    > [<c0102ede>] work_notifysig+0x13/0x19
    >
    > The a_ops->readpages() is nfs_readpages(), and it seems to don't free
    > pages list in error path. So, it hit the
    > BUG_ON(!list_empty(&page_pool)) in __do_page_cache_readahead.

    Wait. Why do we have this insane cleanup semantic anyway? I've just
    grepped through the various readpages() methods out there. None of them
    do anything more sophisticated than to call put_pages_list() in case of
    error, and several of them get that wrong (including NFS, and CIFS).

    Instead of the BUG_ON(), why can't we just stick a put_pages_list() into
    __do_page_cache_readahead() and then get rid of all that duplicated
    error handling in mpage_readpages(), nfs_readpages(), fuse_readpages(),
    etc?

    Cheers,
    Trond
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