[3.19.y-ckt stable] Patch "mm: make sendfile(2) killable" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Thu Nov 12 23:14:47 UTC 2015
This is a note to let you know that I have just added a patch titled
mm: make sendfile(2) killable
to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue
This patch is scheduled to be released in version 3.19.8-ckt10.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From ade284bb40d33fa8325f591f22f659f1f9f0b529 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.com>
Date: Thu, 22 Oct 2015 13:32:21 -0700
Subject: [PATCH 091/120] mm: make sendfile(2) killable
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 at suse.com>
Reported-by: Dmitry Vyukov <dvyukov at google.com>
Cc: Al Viro <viro at ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
mm/filemap.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 673e458..0c95599 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2489,6 +2489,11 @@ 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))
@@ -2526,10 +2531,6 @@ 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;
--
1.9.1
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