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authorJan Kara <jack@suse.com>2015-10-22 13:32:21 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-10-23 17:55:10 +0900
commit296291cdd1629c308114504b850dc343eabc2782 (patch)
tree1d5dad81ebed5a6cc5ccb0d41c9c493894fa8bb8
parent47aee4d8e314384807e98b67ade07f6da476aa75 (diff)
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@suse.com> Reported-by: Dmitry Vyukov <dvyukov@google.com> Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/filemap.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 1cc5467cf36c..327910c2400c 100644
--- a/mm/filemap.c
+++ b/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;