• Vladimir V. Saveliev's avatar
    [PATCH] generic_file_buffered_write(): deadlock on vectored write · 6527c2bd
    Vladimir V. Saveliev authored
    generic_file_buffered_write() prefaults in user pages in order to avoid
    deadlock on copying from the same page as write goes to.
    
    However, it looks like there is a problem when write is vectored:
    fault_in_pages_readable brings in current segment or its part (maxlen).
    OTOH, filemap_copy_from_user_iovec is called to copy number of bytes
    (bytes) which may exceed current segment, so filemap_copy_from_user_iovec
    switches to the next segment which is not brought in yet.  Pagefault is
    generated.  That causes the deadlock if pagefault is for the same page
    write goes to: page being written is locked and not uptodate, pagefault
    will deadlock trying to lock locked page.
    
    [akpm@osdl.org: somewhat rewritten]
    Cc: Neil Brown <neilb@suse.de>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    6527c2bd
filemap.c 63.3 KB