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SubjectRe: 2.0, 2.2, 2.4, 2.5: fsync buffer race
Mikulas Patocka <> wrote:
> Hi
> there's a race condition in filesystem
> let's have a two inodes that are placed in the same buffer.
> call fsync on inode 1
> it goes down to ext2_update_inode [update == 1]
> it calls ll_rw_block at the end
> ll_rw_block starts to write buffer
> ext2_update_inode waits on buffer
> while the buffer is writing, another process calls fsync on inode 2
> it goes again to ext2_update_inode
> it calls ll_rw_block
> ll_rw_block sees buffer locked and exits immediatelly
> ext2_update_inode waits for buffer
> the first write finished, ext2_update_inode exits and changes made by
> second proces to inode 2 ARE NOT WRITTEN TO DISK.

hmm, yes. This is a general weakness in the ll_rw_block() interface. It is
not suitable for data-integrity writeouts, as you've pointed out.

A suitable fix would be do create a new

void wait_and_rw_block(...)

and go use that in all the appropriate places.

I shall make that change for 2.5, thanks.
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