• Jan Kara's avatar
    mm: make sendfile(2) killable · 296291cd
    Jan Kara authored
    Currently a simple program below issues a sendfile(2) system call which
    takes about 62 days to complete in my test KVM instance.
            int fd;
            off_t off = 0;
            fd = open("file", O_RDWR | O_TRUNC | O_SYNC | O_CREAT, 0644);
            ftruncate(fd, 2);
            lseek(fd, 0, SEEK_END);
            sendfile(fd, fd, &off, 0xfffffff);
    Now you should not ask kernel to do a stupid stuff like copying 256MB in
    2-byte chunks and call fsync(2) after each chunk but if you do, sysadmin
    should have a way to stop you.
    We actually do have a check for fatal_signal_pending() in
    generic_perform_write() which triggers in this path however because we
    always succeed in writing something before the check is done, we return
    value > 0 from generic_perform_write() and thus the information about
    signal gets lost.
    Fix the problem by doing the signal check before writing anything.  That
    way generic_perform_write() returns -EINTR, the error gets propagated up
    and the sendfile loop terminates early.
    Signed-off-by: default avatarJan Kara <jack@suse.com>
    Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
    Cc: Al Viro <viro@ZenIV.linux.org.uk>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
filemap.c 70.7 KB