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mm/shmem: report RCU-tasks quiescent states while undoing a range

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This shows up in the Meta fleet on ftruncate() of large tmpfs files:

  INFO: rcu_tasks detected stalls on tasks:
  00000000752fd185: .. nvcsw: 59455/59455 holdout: 1 idle_cpu: -1/0
  task:rocksdb:bottom  state:R  running task
    __folio_split
    find_get_entry
    find_get_entries
    truncate_inode_partial_folio
    shmem_undo_range
    shmem_setattr
    notify_change
    do_ftruncate
    __x64_sys_ftruncate
    do_syscall_64

shmem_undo_range() walks the whole of the requested range in folio_batch
sized steps, twice, and its two cond_resched() calls are the only
reschedule points in that walk.

cond_resched() is not an RCU-tasks quiescent state.  Use
cond_resched_tasks_rcu_qs() at both points so the walk reports an
RCU-tasks quiescent state as it proceeds.

Link: https://lore.kernel.org/20260918-shmem-tasks-rcu-v1-1-79acf91a2569@debian.org
Fixes: 8315f42295 ("rcu: Add call_rcu_tasks()")
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: SJ Park <sj@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Breno Leitao 2026-09-18 04:24:37 -07:00 committed by Andrew Morton
parent d2b82fa39f
commit ebd1a08c19
1 changed files with 2 additions and 2 deletions
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4
mm/shmem.c
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@ -1367,7 +1367,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend,
}
folio_batch_remove_exceptionals(&fbatch);
folio_batch_release(&fbatch);
cond_resched();
cond_resched_tasks_rcu_qs();
}
/*
@ -1408,7 +1408,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend,
index = start;
while (index < end) {
cond_resched();
cond_resched_tasks_rcu_qs();
if (!find_get_entries(mapping, &index, end - 1, &fbatch,
indices)) {