Messages in this thread | | | Date | Wed, 6 Aug 2003 14:42:06 -0700 | From | Andrew Morton <> | Subject | Re: Spurious -EIO when reading a file being written with O_DIRECT? |
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Oleg Drokin <green@namesys.com> wrote: > > We were reported a problem where if a file being written in directio mode > and being read at the same time (in "normal/buffered" mode), then reading > process gets -EIO when near the end of file. > > Initially I thought this is reiserfs-only problemm and digged in that > direction, but then it turned out reiserfs does everything correctly > and the VFS itself seems to be racey (my current suspiction is directio > process uses get_block() that extends the file <schedule> reading process > gets the buffer and submits io, then waits for page to become uptodate > <schedule> direct io process unmaps buffer's metadata > As a result - that page never becomes uptodate and we get -EIO from do_generic_file_read. ) > If I take i_sem around call to do_generic_file_read in generic_file_read (in 2.4.21-pre10), > that of course helps (this is of course not a correct fix, but just a demonstration > that some VFS race is in place). > The same problem can be observed on ext2 in both 2.4.21-pre10 and in 2.6.0-test2 > Attached is test_directio.c program, compile it and run with some filename as argument, > immediately start "tail" with same filename and you'd get almost immediate > I/O error from tail on 2.4 and you'd get same I/O error in 2.6 only after some more waiting. > > Is this something known and expected (or may be somebody have a fix already? ;) )?
Test a current 2.4 kernel - it has lots of redone O_DIRECT-vs-buffered locking.
A 2.6 forward-port of that was done by Badari but I lost it and need to find it again.
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