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authorAl Viro <viro@zeniv.linux.org.uk>2021-05-31 00:32:44 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2021-06-02 17:50:44 -0400
commitbc1bb416bbb9203e250f5c49aaf1d11b5d9c8adb (patch)
tree2d978ab21227c4f1e9de120f1ecab5b110e56144 /mm/filemap.c
parent9067931236651c8bde847d17a2f862d052e672b7 (diff)
generic_perform_write()/iomap_write_actor(): saner logics for short copy
if we run into a short copy and ->write_end() refuses to advance at all, use the amount we'd managed to copy for the next iteration to handle. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'mm/filemap.c')
-rw-r--r--mm/filemap.c24
1 files changed, 9 insertions, 15 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 66f7e9fdfbc4..0be24942bf8e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3642,10 +3642,6 @@ again:
* Otherwise there's a nasty deadlock on copying from the
* same page as we're writing to, without it being marked
* up-to-date.
- *
- * Not only is this an optimisation, but it is also required
- * to check that the address is actually valid, when atomic
- * usercopies are used, below.
*/
if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
status = -EFAULT;
@@ -3672,24 +3668,22 @@ again:
page, fsdata);
if (unlikely(status < 0))
break;
- copied = status;
cond_resched();
- iov_iter_advance(i, copied);
- if (unlikely(copied == 0)) {
+ if (unlikely(status == 0)) {
/*
- * If we were unable to copy any data at all, we must
- * fall back to a single segment length write.
- *
- * If we didn't fallback here, we could livelock
- * because not all segments in the iov can be copied at
- * once without a pagefault.
+ * A short copy made ->write_end() reject the
+ * thing entirely. Might be memory poisoning
+ * halfway through, might be a race with munmap,
+ * might be severe memory pressure.
*/
- bytes = min_t(unsigned long, PAGE_SIZE - offset,
- iov_iter_single_seg_count(i));
+ if (copied)
+ bytes = copied;
goto again;
}
+ copied = status;
+ iov_iter_advance(i, copied);
pos += copied;
written += copied;