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    SubjectRe: [PATCH] remove BUG() in possible but rare condition
    On Wed 11-04-12 14:12:44, Andrew Morton wrote:
    > On Wed, 11 Apr 2012 17:51:57 -0300
    > Glauber Costa <glommer@parallels.com> wrote:
    >
    > > On 04/11/2012 05:26 PM, Andrew Morton wrote:
    > > >>
    > > >> > failed:
    > > >> > - BUG();
    > > >> > unlock_page(page);
    > > >> > page_cache_release(page);
    > > >> > return NULL;
    > > > Cute.
    > > >
    > > > AFAICT what happened was that in my April 2002 rewrite of this code I
    > > > put a non-fatal buffer_error() warning in that case to tell us that
    > > > something bad happened.
    > > >
    > > > Years later we removed the temporary buffer_error() and mistakenly
    > > > replaced that warning with a BUG(). Only it*can* happen.
    > > >
    > > > We can remove the BUG() and fix up callers, or we can pass retry=1 into
    > > > alloc_page_buffers(), so grow_dev_page() "cannot fail". Immortal
    > > > functions are a silly fiction, so we should remove the BUG() and fix up
    > > > callers.
    > > >
    > > Any particular caller you are concerned with ?
    >
    > Didn't someone see a buggy caller in btrfs?

    No I missed that __getblk (__getblk_slow) returns NULL only if
    grow_buffers < 0 while it returns 0 for the allocation failure.

    Sorry for confusion.
    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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