kernel/linux.git/fs/netfs/write_issue.c, branch v7.1-rc5

netfs, afs: Fix write skipping in dir/link writepages

2026-05-12T12:42:32+00:00

Fix netfs_write_single() and afs_single_writepages() to better handle a write that would be skipped due to lock contention and WB_SYNC_NONE by returning 1 from netfs_write_single() if it skipped and making afs_single_writepages() skip also. If a skip occurs, the inode must be re-marked as the VFS may have cleared the mark. This is really only theoretical for directories in netfs_write_single() as the only path to that is through afs_single_writepages() that takes the ->validate_lock around it, thereby serialising it. Fixes: 6dd80936618c ("afs: Use netfslib for directories") Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-24-dhowells@redhat.com cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix potential deadlock in write-through mode

2026-05-12T12:42:31+00:00

Fix netfs_advance_writethrough() to always unlock the supplied folio and to mark it dirty if it isn't yet written to the end. Unfortunately, it can't be marked for writeback until the folio is done with as that may cause a deadlock against mmapped reads and writes. Even though it has been marked dirty, premature writeback can't occur as the caller is holding both inode->i_rwsem (which will prevent concurrent truncation, fallocation, DIO and other writes) and ictx->wb_lock (which will cause flushing to wait and writeback to skip or wait). Note that this may be easier to deal with once the queuing of folios is split from the generation of subrequests. Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Closes: https://sashiko.dev/#/patchset/20260427154639.180684-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-15-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix missing barriers when accessing stream->subrequests locklessly

2026-05-12T12:42:29+00:00

The list of subrequests attached to stream->subrequests is accessed without locks by netfs_collect_read_results() and netfs_collect_write_results(), and then they access subreq->flags without taking a barrier after getting the subreq pointer from the list. Relatedly, the functions that build the list don't use any sort of write barrier when constructing the list to make sure that the NETFS_SREQ_IN_PROGRESS flag is perceived to be set first if no lock is taken. Fix this by: (1) Add a new list_add_tail_release() function that uses a release barrier to set the pointer to the new member of the list. (2) Add a new list_first_entry_or_null_acquire() function that uses an acquire barrier to read the pointer to the first member in a list (or return NULL). (3) Use list_add_tail_release() when adding a subreq to ->subrequests. (4) Use list_first_entry_or_null_acquire() when initially accessing the front of the list (when an item is removed, the pointer to the new front iterm is obtained under the same lock). Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Link: https://sashiko.dev/#/patchset/20260326104544.509518-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-4-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix the handling of stream->front by removing it

2026-03-26T14:18:45+00:00

The netfs_io_stream::front member is meant to point to the subrequest currently being collected on a stream, but it isn't actually used this way by direct write (which mostly ignores it). However, there's a tracepoint which looks at it. Further, stream->front is actually redundant with stream->subrequests.next. Fix the potential problem in the direct code by just removing the member and using stream->subrequests.next instead, thereby also simplifying the code. Fixes: a0b4c7a49137 ("netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence") Reported-by: Paulo Alcantara Signed-off-by: David Howells Link: https://patch.msgid.link/4158599.1774426817@warthog.procyon.org.uk Reviewed-by: Paulo Alcantara (Red Hat) cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence

2026-02-26T13:44:32+00:00

Fix netfslib such that when it's making an unbuffered or DIO write, to make sure that it sends each subrequest strictly sequentially, waiting till the previous one is 'committed' before sending the next so that we don't have pieces landing out of order and potentially leaving a hole if an error occurs (ENOSPC for example). This is done by copying in just those bits of issuing, collecting and retrying subrequests that are necessary to do one subrequest at a time. Retrying, in particular, is simpler because if the current subrequest needs retrying, the source iterator can just be copied again and the subrequest prepped and issued again without needing to be concerned about whether it needs merging with the previous or next in the sequence. Note that the issuing loop waits for a subrequest to complete right after issuing it, but this wait could be moved elsewhere allowing preparatory steps to be performed whilst the subrequest is in progress. In particular, once content encryption is available in netfslib, that could be done whilst waiting, as could cleanup of buffers that have been completed. Fixes: 153a9961b551 ("netfs: Implement unbuffered/DIO write support") Signed-off-by: David Howells Link: https://patch.msgid.link/58526.1772112753@warthog.procyon.org.uk Tested-by: Steve French Reviewed-by: Paulo Alcantara (Red Hat) cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: when subreq is marked for retry, do not check if it faced an error

2026-02-08T23:07:43+00:00

The *_subreq_terminated functions today only process the NEED_RETRY flag when the subreq was successful or failed with EAGAIN error. However, there could be other retriable errors for network filesystems. Avoid this by processing the NEED_RETRY irrespective of the error code faced by the subreq. If it was specifically marked for retry, the error code must not matter. Acked-by: David Howells Signed-off-by: Shyam Prasad N Signed-off-by: Steve French

netfs: fix reference leak

2025-09-26T08:14:19+00:00

Commit 20d72b00ca81 ("netfs: Fix the request's work item to not require a ref") modified netfs_alloc_request() to initialize the reference counter to 2 instead of 1. The rationale was that the requet's "work" would release the second reference after completion (via netfs_{read,write}_collection_worker()). That works most of the time if all goes well. However, it leaks this additional reference if the request is released before the I/O operation has been submitted: the error code path only decrements the reference counter once and the work item will never be queued because there will never be a completion. This has caused outages of our whole server cluster today because tasks were blocked in netfs_wait_for_outstanding_io(), leading to deadlocks in Ceph (another bug that I will address soon in another patch). This was caused by a netfs_pgpriv2_begin_copy_to_cache() call which failed in fscache_begin_write_operation(). The leaked netfs_io_request was never completed, leaving `netfs_inode.io_count` with a positive value forever. All of this is super-fragile code. Finding out which code paths will lead to an eventual completion and which do not is hard to see: - Some functions like netfs_create_write_req() allocate a request, but will never submit any I/O. - netfs_unbuffered_read_iter_locked() calls netfs_unbuffered_read() and then netfs_put_request(); however, netfs_unbuffered_read() can also fail early before submitting the I/O request, therefore another netfs_put_request() call must be added there. A rule of thumb is that functions that return a `netfs_io_request` do not submit I/O, and all of their callers must be checked. For my taste, the whole netfs code needs an overhaul to make reference counting easier to understand and less fragile & obscure. But to fix this bug here and now and produce a patch that is adequate for a stable backport, I tried a minimal approach that quickly frees the request object upon early failure. I decided against adding a second netfs_put_request() each time because that would cause code duplication which obscures the code further. Instead, I added the function netfs_put_failed_request() which frees such a failed request synchronously under the assumption that the reference count is exactly 2 (as initially set by netfs_alloc_request() and never touched), verified by a WARN_ON_ONCE(). It then deinitializes the request object (without going through the "cleanup_work" indirection) and frees the allocation (with RCU protection to protect against concurrent access by netfs_requests_seq_start()). All code paths that fail early have been changed to call netfs_put_failed_request() instead of netfs_put_request(). Additionally, I have added a netfs_put_request() call to netfs_unbuffered_read() as explained above because the netfs_put_failed_request() approach does not work there. Fixes: 20d72b00ca81 ("netfs: Fix the request's work item to not require a ref") Signed-off-by: Max Kellermann Signed-off-by: David Howells cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org cc: stable@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix unbuffered write error handling

2025-08-15T13:56:49+00:00

If all the subrequests in an unbuffered write stream fail, the subrequest collector doesn't update the stream->transferred value and it retains its initial LONG_MAX value. Unfortunately, if all active streams fail, then we take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set in wreq->transferred - which is then returned from ->write_iter(). LONG_MAX was chosen as the initial value so that all the streams can be quickly assessed by taking the smallest value of all stream->transferred - but this only works if we've set any of them. Fix this by adding a flag to indicate whether the value in stream->transferred is valid and checking that when we integrate the values. stream->transferred can then be initialised to zero. This was found by running the generic/750 xfstest against cifs with cache=none. It splices data to the target file. Once (if) it has used up all the available scratch space, the writes start failing with ENOSPC. This causes ->write_iter() to fail. However, it was returning wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought the amount transferred was non-zero) and iter_file_splice_write() would then try to clean up that amount of pipe bufferage - leading to an oops when it overran. The kernel log showed: CIFS: VFS: Send error in write = -28 followed by: BUG: kernel NULL pointer dereference, address: 0000000000000008 with: RIP: 0010:iter_file_splice_write+0x3a4/0x520 do_splice+0x197/0x4e0 or: RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282) iter_file_splice_write (fs/splice.c:755) Also put a warning check into splice to announce if ->write_iter() returned that it had written more than it was asked to. Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Reported-by: Xiaoli Feng Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220445 Signed-off-by: David Howells Link: https://lore.kernel.org/915443.1755207950@warthog.procyon.org.uk cc: Paulo Alcantara cc: Steve French cc: Shyam Prasad N cc: netfs@lists.linux.dev cc: linux-cifs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org cc: stable@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix wait/wake to be consistent about the waitqueue used

2025-05-21T12:35:21+00:00

Fix further inconsistencies in the use of waitqueues (clear_and_wake_up_bit() vs private waitqueue). Move some of this stuff from the read and write sides into common code so that it can be done in fewer places. To make this work, async I/O needs to set NETFS_RREQ_OFFLOAD_COLLECTION to indicate that a workqueue will do the collecting and places that call the wait function need to deal with it returning the amount transferred. Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Signed-off-by: David Howells Link: https://lore.kernel.org/20250519090707.2848510-5-dhowells@redhat.com cc: Marc Dionne cc: Steve French cc: Ihor Solodrai cc: Eric Van Hensbergen cc: Latchesar Ionkov cc: Dominique Martinet cc: Christian Schoenebeck cc: Paulo Alcantara cc: Jeff Layton cc: v9fs@lists.linux.dev cc: linux-cifs@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner

netfs: Fix the request's work item to not require a ref

2025-05-21T12:35:20+00:00

When the netfs_io_request struct's work item is queued, it must be supplied with a ref to the work item struct to prevent it being deallocated whilst on the queue or whilst it is being processed. This is tricky to manage as we have to get a ref before we try and queue it and then we may find it's already queued and is thus already holding a ref - in which case we have to try and get rid of the ref again. The problem comes if we're in BH or IRQ context and need to drop the ref: if netfs_put_request() reduces the count to 0, we have to do the cleanup - but the cleanup may need to wait. Fix this by adding a new work item to the request, ->cleanup_work, and dispatching that when the refcount hits zero. That can then synchronously cancel any outstanding work on the main work item before doing the cleanup. Adding a new work item also deals with another problem upstream where it's sometimes changing the work func in the put function and requeuing it - which has occasionally in the past caused the cleanup to happen incorrectly. As a bonus, this allows us to get rid of the 'was_async' parameter from a bunch of functions. This indicated whether the put function might not be permitted to sleep. Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers") Signed-off-by: David Howells Link: https://lore.kernel.org/20250519090707.2848510-4-dhowells@redhat.com cc: Paulo Alcantara cc: Marc Dionne cc: Steve French cc: linux-cifs@vger.kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner