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Date: Sun, 15 Nov 2015 01:45:45 +0000 From: Ben Hutchings <ben@...adent.org.uk> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org CC: akpm@...ux-foundation.org, "Dmitry Vyukov" <dvyukov@...gle.com>, "Linus Torvalds" <torvalds@...ux-foundation.org>, "Jan Kara" <jack@...e.com>, "Al Viro" <viro@...IV.linux.org.uk> Subject: [PATCH 3.2 41/60] mm: make sendfile(2) killable 3.2.73-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jan Kara <jack@...e.com> commit 296291cdd1629c308114504b850dc343eabc2782 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: Jan Kara <jack@...e.com> Reported-by: Dmitry Vyukov <dvyukov@...gle.com> Cc: Al Viro <viro@...IV.linux.org.uk> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> Signed-off-by: Ben Hutchings <ben@...adent.org.uk> --- mm/filemap.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2408,6 +2408,11 @@ 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)) @@ -2448,10 +2453,6 @@ 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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