kernel/git/stable/linux-stable.git/fs/netfs/write_issue.c, branch master

netfs: break unbuffered write when netfs_alloc_subrequest() fails

2026-08-31T07:54:38+00:00

syzbot reported a null-ptr-deref below [1] following a fault injection in netfs_alloc_subrequest(). [0] When netfs_alloc_subrequest() fails, subreq is NULL. Later, netfs_prepare_write() tries to initialize members of subreq(e.g., source), the issue in [1] is triggered. Let's handle the error of netfs_prepare_write() properly. [0] FAULT_INJECTION: forcing a failure. name failslab, interval 1, probability 0, space 0, times 0 Call Trace: netfs_alloc_subrequest+0x116/0x3f0 netfs_prepare_write+0x76/0x7b0 netfs_unbuffered_write+0x75c/0x2020 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 netfs_unbuffered_write_iter+0x442/0x720 v9fs_file_write_iter+0xbf/0x100 vfs_write+0x6ac/0x1050 [1] KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af] RIP: 0010:netfs_prepare_write+0xbc/0x7b0 fs/netfs/write_issue.c:173 Call Trace: netfs_unbuffered_write+0x75c/0x2020 fs/netfs/direct_write.c:111 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 fs/netfs/direct_write.c:290 netfs_unbuffered_write_iter+0x442/0x720 fs/netfs/direct_write.c:382 v9fs_file_write_iter+0xbf/0x100 fs/9p/vfs_file.c:409 new_sync_write fs/read_write.c:595 [inline] Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Reported-by: syzbot+6a13fc77eb6f0802be2d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6a13fc77eb6f0802be2d Tested-by: syzbot+6a13fc77eb6f0802be2d@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis Signed-off-by: David Howells Link: https://patch.msgid.link/20260827134304.2075713-7-dhowells@redhat.com Acked-by: Paulo Alcantara Signed-off-by: Christian Brauner (Amutable)

netfs: Fix folio_queue ENOMEM in writeback by adding a mempool

2026-07-28T13:42:31+00:00

Fix the handling of folio_queue allocation failure in writeback by adding a mempool and passing in gfp_t flags to the rolling buffer functions that allocate memory, using the mempool if gfp != GFP_KERNEL. This is then extended upwards and the gfp to be used for a request is stored in the netfs_io_request struct and is then used for both requests and subrequests, eliminating the sleeping loops there. The failure caused: folio != NULL WARNING: fs/netfs/write_issue.c:603 at netfs_writepages+0x883/0xa10 fs/netfs/write_issue.c:603, CPU#3: syz.0.17/5919 Fixes: cd0277ed0c18 ("netfs: Use new folio_queue data type and iterator instead of xarray iter") Reported-by: syzbot+0da43efa72f88bd3a8af@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=0da43efa72f88bd3a8af Signed-off-by: David Howells Link: https://patch.msgid.link/20260727130716.1099906-5-dhowells@redhat.com Tested-by: syzbot+0da43efa72f88bd3a8af@syzkaller.appspotmail.com cc: Paulo Alcantara cc: Yun Zhou cc: Matthew Wilcox cc: Christoph Hellwig cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: handle single writeback rolling buffer allocation failure

2026-07-28T13:42:31+00:00

netfs_write_folio_single() takes an extra folio reference before appending the folio to the rolling buffer. rolling_buffer_append() can fail if it cannot allocate another folio_queue. Check the return value and drop the extra folio reference before returning the error. Fixes: 49866ce7ea8d ("netfs: Add support for caching single monolithic objects such as AFS dirs") Signed-off-by: Yichong Chen Signed-off-by: David Howells Link: https://patch.msgid.link/20260727130716.1099906-3-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: Fix folio state after ENOMEM whilst under writeback iteration

2026-07-01T13:26:30+00:00

Fix the state of the current folio when ENOMEM occurs during writeback iteration. The folio needs to be redirtied and unlocked before the terminal writeback_iter() is invoked. Fixes: 06fa229ceb36 ("netfs: Abstract out a rolling folio buffer implementation") Link: https://sashiko.dev/#/patchset/20260619140646.2633762-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260625140640.3116900-15-dhowells@redhat.com cc: Paulo Alcantara cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: Fix writeback error handling

2026-07-01T13:26:30+00:00

Fix the error handling in writeback_iter() loop. If an error occurs, writeback_iter() needs to be called again with *error set to the error so that it can clean up iteration state. Further, the current folio needs unlocking and redirtying. Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Link: https://sashiko.dev/#/patchset/20260619140646.2633762-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260625140640.3116900-14-dhowells@redhat.com cc: Paulo Alcantara cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: Fix writethrough to use collection offload

2026-07-01T13:26:30+00:00

Fix writethrough write to set NETFS_RREQ_OFFLOAD_COLLECTION on the request so that collection is processed asynchronously rather than only right at the end - and also so that asynchronous O_SYNC writes get collected at all. Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Closes: https://sashiko.dev/#/patchset/20260616100821.2062304-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260625140640.3116900-13-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: Replace wb_lock with a bit lock for asynchronicity

2026-07-01T13:26:29+00:00

The netfs_inode::wb_lock mutex is used to prevent multiple simultaneous writebacks from fighting each other (a writeback thread will write multiple discontiguous regions within the same request). The mutex, however, only serialises the issuing of subrequests; it doesn't serialise the collection of results, and, in particular, the updating of file size information and fscache populatedness data. Unfortunately, the mutex cannot be held around the entire process as it has to be unlocked in the same thread in which it is locked - and we don't want to hold up the allocator whilst we complete the writeback. Fix this by replacing the mutex with a bit flag and a list of lock waiters so that the lock can be dropped in the collector thread after collection is complete. Link: https://sashiko.dev/#/patchset/20260608145432.681865-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260625140640.3116900-12-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

netfs: Fix netfs_create_write_req() to handle async cache object creation

2026-07-01T13:26:28+00:00

netfs_create_write_req() will skip caching if the fscache cookie is disabled, but this is a problem because async cache object creation might not have got far enough yet that has been enabled - thereby causing the call to fscache_begin_write_operation() to be skipped. Fix this by removing the checks on the cookie and delegating this to fscache_begin_write_operation(). Fixes: 7b589a9b45ae ("netfs: Fix handling of USE_PGPRIV2 and WRITE_TO_CACHE flags") Closes: https://sashiko.dev/#/patchset/20260624115737.2964520-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260625140640.3116900-3-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Amutable)

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