From: Jan Kara <jack@xxxxxxxx>
Subject: mm: make sendfile(2) killable
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: Jan Kara <jack@xxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff -puN mm/filemap.c~mm-make-sendfile2-killable mm/filemap.c
--- a/mm/filemap.c~mm-make-sendfile2-killable
+++ a/mm/filemap.c
@@ -2488,6 +2488,11 @@ again:
break;
}
+ if (fatal_signal_pending(current)) {
+ status = -EINTR;
+ break;
+ }
+
status = a_ops->write_begin(file, mapping, pos, bytes, flags,
&page, &fsdata);
if (unlikely(status < 0))
@@ -2525,10 +2530,6 @@ again:
written += copied;
balance_dirty_pages_ratelimited(mapping);
- if (fatal_signal_pending(current)) {
- status = -EINTR;
- break;
- }
} while (iov_iter_count(i));
return written ? written : status;
_
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