4.19-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 4ea899ead2786a30aaa8181fefa81a3df4ad28f6 ]
Introduce a local wait_for_completion variable to avoid an access to the potentially freed dio struture after dropping the last reference count.
Also use the chance to document the completion behavior to make the refcounting clear to the reader of the code.
Fixes: ff6a9292e6 ("iomap: implement direct I/O") Reported-by: Chandan Rajendra chandan@linux.ibm.com Reported-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Christoph Hellwig hch@lst.de Tested-by: Chandan Rajendra chandan@linux.ibm.com Tested-by: Darrick J. Wong darrick.wong@oracle.com Reviewed-by: Dave Chinner dchinner@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/iomap.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/fs/iomap.c b/fs/iomap.c index 2e3e64012db7..fac45206418a 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -1787,6 +1787,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, loff_t pos = iocb->ki_pos, start = pos; loff_t end = iocb->ki_pos + count - 1, ret = 0; unsigned int flags = IOMAP_DIRECT; + bool wait_for_completion = is_sync_kiocb(iocb); struct blk_plug plug; struct iomap_dio *dio;
@@ -1806,7 +1807,6 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, dio->end_io = end_io; dio->error = 0; dio->flags = 0; - dio->wait_for_completion = is_sync_kiocb(iocb);
dio->submit.iter = iter; dio->submit.waiter = current; @@ -1861,7 +1861,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, dio_warn_stale_pagecache(iocb->ki_filp); ret = 0;
- if (iov_iter_rw(iter) == WRITE && !dio->wait_for_completion && + if (iov_iter_rw(iter) == WRITE && !wait_for_completion && !inode->i_sb->s_dio_done_wq) { ret = sb_init_dio_done_wq(inode->i_sb); if (ret < 0) @@ -1877,7 +1877,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, if (ret <= 0) { /* magic error code to fall back to buffered I/O */ if (ret == -ENOTBLK) { - dio->wait_for_completion = true; + wait_for_completion = true; ret = 0; } break; @@ -1899,8 +1899,24 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, if (dio->flags & IOMAP_DIO_WRITE_FUA) dio->flags &= ~IOMAP_DIO_NEED_SYNC;
+ /* + * We are about to drop our additional submission reference, which + * might be the last reference to the dio. There are three three + * different ways we can progress here: + * + * (a) If this is the last reference we will always complete and free + * the dio ourselves. + * (b) If this is not the last reference, and we serve an asynchronous + * iocb, we must never touch the dio after the decrement, the + * I/O completion handler will complete and free it. + * (c) If this is not the last reference, but we serve a synchronous + * iocb, the I/O completion handler will wake us up on the drop + * of the final reference, and we will complete and free it here + * after we got woken by the I/O completion handler. + */ + dio->wait_for_completion = wait_for_completion; if (!atomic_dec_and_test(&dio->ref)) { - if (!dio->wait_for_completion) + if (!wait_for_completion) return -EIOCBQUEUED;
for (;;) { @@ -1917,9 +1933,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, __set_current_state(TASK_RUNNING); }
- ret = iomap_dio_complete(dio); - - return ret; + return iomap_dio_complete(dio);
out_free_dio: kfree(dio);