mm: make sendfile(2) killable
commit 296291cdd1
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@suse.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
wifi-calibration
parent
bd69119dc8
commit
6c0da28df5
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@ -2461,6 +2461,11 @@ again:
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break;
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}
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if (fatal_signal_pending(current)) {
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status = -EINTR;
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break;
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}
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status = a_ops->write_begin(file, mapping, pos, bytes, flags,
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&page, &fsdata);
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if (unlikely(status < 0))
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@ -2498,10 +2503,6 @@ again:
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written += copied;
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balance_dirty_pages_ratelimited(mapping);
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if (fatal_signal_pending(current)) {
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status = -EINTR;
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break;
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}
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} while (iov_iter_count(i));
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return written ? written : status;
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