The patch titled Subject: nilfs2: fix potential hang in nilfs_detach_log_writer() has been added to the -mm mm-hotfixes-unstable branch. Its filename is nilfs2-fix-potential-hang-in-nilfs_detach_log_writer.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Ryusuke Konishi konishi.ryusuke@gmail.com Subject: nilfs2: fix potential hang in nilfs_detach_log_writer() Date: Mon, 20 May 2024 22:26:21 +0900
Syzbot has reported a potential hang in nilfs_detach_log_writer() called during nilfs2 unmount.
Analysis revealed that this is because nilfs_segctor_sync(), which synchronizes with the log writer thread, can be called after nilfs_segctor_destroy() terminates that thread, as shown in the call trace below:
nilfs_detach_log_writer nilfs_segctor_destroy nilfs_segctor_kill_thread --> Shut down log writer thread flush_work nilfs_iput_work_func nilfs_dispose_list iput nilfs_evict_inode nilfs_transaction_commit nilfs_construct_segment (if inode needs sync) nilfs_segctor_sync --> Attempt to synchronize with log writer thread *** DEADLOCK ***
Fix this issue by changing nilfs_segctor_sync() so that the log writer thread returns normally without synchronizing after it terminates, and by forcing tasks that are already waiting to complete once after the thread terminates.
The skipped inode metadata flushout will then be processed together in the subsequent cleanup work in nilfs_segctor_destroy().
Link: https://lkml.kernel.org/r/20240520132621.4054-4-konishi.ryusuke@gmail.com Signed-off-by: Ryusuke Konishi konishi.ryusuke@gmail.com Reported-by: syzbot+e3973c409251e136fdd0@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=e3973c409251e136fdd0 Tested-by: Ryusuke Konishi konishi.ryusuke@gmail.com Cc: stable@vger.kernel.org Cc: "Bai, Shuangpeng" sjb7183@psu.edu Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
fs/nilfs2/segment.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)
--- a/fs/nilfs2/segment.c~nilfs2-fix-potential-hang-in-nilfs_detach_log_writer +++ a/fs/nilfs2/segment.c @@ -2190,6 +2190,14 @@ static int nilfs_segctor_sync(struct nil for (;;) { set_current_state(TASK_INTERRUPTIBLE);
+ /* + * Synchronize only while the log writer thread is alive. + * Leave flushing out after the log writer thread exits to + * the cleanup work in nilfs_segctor_destroy(). + */ + if (!sci->sc_task) + break; + if (atomic_read(&wait_req.done)) { err = wait_req.err; break; @@ -2205,7 +2213,7 @@ static int nilfs_segctor_sync(struct nil return err; }
-static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err) +static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err, bool force) { struct nilfs_segctor_wait_request *wrq, *n; unsigned long flags; @@ -2213,7 +2221,7 @@ static void nilfs_segctor_wakeup(struct spin_lock_irqsave(&sci->sc_wait_request.lock, flags); list_for_each_entry_safe(wrq, n, &sci->sc_wait_request.head, wq.entry) { if (!atomic_read(&wrq->done) && - nilfs_cnt32_ge(sci->sc_seq_done, wrq->seq)) { + (force || nilfs_cnt32_ge(sci->sc_seq_done, wrq->seq))) { wrq->err = err; atomic_set(&wrq->done, 1); } @@ -2362,7 +2370,7 @@ static void nilfs_segctor_notify(struct if (mode == SC_LSEG_SR) { sci->sc_state &= ~NILFS_SEGCTOR_COMMIT; sci->sc_seq_done = sci->sc_seq_accepted; - nilfs_segctor_wakeup(sci, err); + nilfs_segctor_wakeup(sci, err, false); sci->sc_flush_request = 0; } else { if (mode == SC_FLUSH_FILE) @@ -2746,6 +2754,13 @@ static void nilfs_segctor_destroy(struct || sci->sc_seq_request != sci->sc_seq_done); spin_unlock(&sci->sc_state_lock);
+ /* + * Forcibly wake up tasks waiting in nilfs_segctor_sync(), which can + * be called from delayed iput() via nilfs_evict_inode() and can race + * with the above log writer thread termination. + */ + nilfs_segctor_wakeup(sci, 0, true); + if (flush_work(&sci->sc_iput_work)) flag = true;
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Patches currently in -mm which might be from konishi.ryusuke@gmail.com are
nilfs2-fix-use-after-free-of-timer-for-log-writer-thread.patch nilfs2-fix-unexpected-freezing-of-nilfs_segctor_sync.patch nilfs2-fix-potential-hang-in-nilfs_detach_log_writer.patch