| Message ID | e1cb4f8981f8c6e7e0384e95faf1911d9937e979.1697647960.git.jstancek@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] iomap: fix short copy in iomap_write_iter() | expand |
On Wed, Oct 18, 2023 at 08:32:32PM +0200, Jan Stancek wrote: > Starting with commit 5d8edfb900d5 ("iomap: Copy larger chunks from > userspace"), iomap_write_iter() can get into endless loop. This can > be reproduced with LTP writev07 which uses partially valid iovecs: > struct iovec wr_iovec[] = { > { buffer, 64 }, > { bad_addr, 64 }, > { buffer + 64, 64 }, > { buffer + 64 * 2, 64 }, > }; > > commit bc1bb416bbb9 ("generic_perform_write()/iomap_write_actor(): > saner logics for short copy") previously introduced the logic, which > made short copy retry in next iteration with amount of "bytes" it > managed to copy: > > if (unlikely(status == 0)) { > /* > * A short copy made iomap_write_end() reject the > * thing entirely. Might be memory poisoning > * halfway through, might be a race with munmap, > * might be severe memory pressure. > */ > if (copied) > bytes = copied; > > However, since 5d8edfb900d5 "bytes" is no longer carried into next > iteration, because it is now always initialized at the beginning of > the loop. And for iov_iter_count < PAGE_SIZE, "bytes" ends up with > same value as previous iteration, making the loop retry same copy > over and over, which leads to writev07 testcase hanging. > > Make next iteration retry with amount of bytes we managed to copy. > > Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") > Signed-off-by: Jan Stancek <jstancek@redhat.com> Looks fine to me, will send it out for testing... Reviewed-by: Darrick J. Wong <djwong@kernel.org> --D > --- > Changes in v2: > - use goto instead of new variable (suggested by Christoph Hellwig) > > fs/iomap/buffered-io.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index 5db54ca29a35..2bc0aa23fde3 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -881,8 +881,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) > size_t bytes; /* Bytes to write to folio */ > size_t copied; /* Bytes copied from user */ > > + bytes = iov_iter_count(i); > +retry: > offset = pos & (chunk - 1); > - bytes = min(chunk - offset, iov_iter_count(i)); > + bytes = min(chunk - offset, bytes); > status = balance_dirty_pages_ratelimited_flags(mapping, > bdp_flags); > if (unlikely(status)) > @@ -933,10 +935,12 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) > * halfway through, might be a race with munmap, > * might be severe memory pressure. > */ > - if (copied) > - bytes = copied; > if (chunk > PAGE_SIZE) > chunk /= 2; > + if (copied) { > + bytes = copied; > + goto retry; > + } > } else { > pos += status; > written += status; > -- > 2.31.1 >
Looks good:
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 5db54ca29a35..2bc0aa23fde3 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -881,8 +881,10 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) size_t bytes; /* Bytes to write to folio */ size_t copied; /* Bytes copied from user */ + bytes = iov_iter_count(i); +retry: offset = pos & (chunk - 1); - bytes = min(chunk - offset, iov_iter_count(i)); + bytes = min(chunk - offset, bytes); status = balance_dirty_pages_ratelimited_flags(mapping, bdp_flags); if (unlikely(status)) @@ -933,10 +935,12 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i) * halfway through, might be a race with munmap, * might be severe memory pressure. */ - if (copied) - bytes = copied; if (chunk > PAGE_SIZE) chunk /= 2; + if (copied) { + bytes = copied; + goto retry; + } } else { pos += status; written += status;
Starting with commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace"), iomap_write_iter() can get into endless loop. This can be reproduced with LTP writev07 which uses partially valid iovecs: struct iovec wr_iovec[] = { { buffer, 64 }, { bad_addr, 64 }, { buffer + 64, 64 }, { buffer + 64 * 2, 64 }, }; commit bc1bb416bbb9 ("generic_perform_write()/iomap_write_actor(): saner logics for short copy") previously introduced the logic, which made short copy retry in next iteration with amount of "bytes" it managed to copy: if (unlikely(status == 0)) { /* * A short copy made iomap_write_end() reject the * thing entirely. Might be memory poisoning * halfway through, might be a race with munmap, * might be severe memory pressure. */ if (copied) bytes = copied; However, since 5d8edfb900d5 "bytes" is no longer carried into next iteration, because it is now always initialized at the beginning of the loop. And for iov_iter_count < PAGE_SIZE, "bytes" ends up with same value as previous iteration, making the loop retry same copy over and over, which leads to writev07 testcase hanging. Make next iteration retry with amount of bytes we managed to copy. Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") Signed-off-by: Jan Stancek <jstancek@redhat.com> --- Changes in v2: - use goto instead of new variable (suggested by Christoph Hellwig) fs/iomap/buffered-io.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)