Commit 475a2300 authored by Jan Kara's avatar Jan Kara Committed by Luis Henriques

mm: make sendfile(2) killable

commit 296291cd upstream.

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>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 61e709be
...@@ -2462,6 +2462,11 @@ ssize_t generic_perform_write(struct file *file, ...@@ -2462,6 +2462,11 @@ ssize_t generic_perform_write(struct file *file,
break; break;
} }
if (fatal_signal_pending(current)) {
status = -EINTR;
break;
}
status = a_ops->write_begin(file, mapping, pos, bytes, flags, status = a_ops->write_begin(file, mapping, pos, bytes, flags,
&page, &fsdata); &page, &fsdata);
if (unlikely(status < 0)) if (unlikely(status < 0))
...@@ -2499,10 +2504,6 @@ ssize_t generic_perform_write(struct file *file, ...@@ -2499,10 +2504,6 @@ ssize_t generic_perform_write(struct file *file,
written += copied; written += copied;
balance_dirty_pages_ratelimited(mapping); balance_dirty_pages_ratelimited(mapping);
if (fatal_signal_pending(current)) {
status = -EINTR;
break;
}
} while (iov_iter_count(i)); } while (iov_iter_count(i));
return written ? written : status; return written ? written : status;
......
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