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io_uring/tctx: work around xa_store() allocation error issue

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JIRA: https://issues.redhat.com/browse/RHEL-105612

commit 7eb75ce7527129d7f1fee6951566af409a37a1c4
Author: Jens Axboe <axboe@kernel.dk>
Date:   Fri Nov 29 07:20:28 2024 -0700

    io_uring/tctx: work around xa_store() allocation error issue
    
    syzbot triggered the following WARN_ON:
    
    WARNING: CPU: 0 PID: 16 at io_uring/tctx.c:51 __io_uring_free+0xfa/0x140 io_uring/tctx.c:51
    
    which is the
    
    WARN_ON_ONCE(!xa_empty(&tctx->xa));
    
    sanity check in __io_uring_free() when a io_uring_task is going through
    its final put. The syzbot test case includes injecting memory allocation
    failures, and it very much looks like xa_store() can fail one of its
    memory allocations and end up with ->head being non-NULL even though no
    entries exist in the xarray.
    
    Until this issue gets sorted out, work around it by attempting to
    iterate entries in our xarray, and WARN_ON_ONCE() if one is found.
    
    Reported-by: syzbot+cc36d44ec9f368e443d3@syzkaller.appspotmail.com
    Link: https://lore.kernel.org/io-uring/673c1643.050a0220.87769.0066.GAE@google.com/
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
This commit is contained in:
Jeff Moyer
2025-10-25 21:21:37 -04:00
parent 8bb9d14811
commit acf4fd674f
1 changed files with 12 additions and 1 deletions
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io_uring/tctx.c
+12 -1
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@@ -47,8 +47,19 @@ static struct io_wq *io_init_wq_offload(struct io_ring_ctx *ctx,
void __io_uring_free(struct task_struct *tsk)
{
struct io_uring_task *tctx = tsk->io_uring;
struct io_tctx_node *node;
unsigned long index;
WARN_ON_ONCE(!xa_empty(&tctx->xa));
/*
* Fault injection forcing allocation errors in the xa_store() path
* can lead to xa_empty() returning false, even though no actual
* node is stored in the xarray. Until that gets sorted out, attempt
* an iteration here and warn if any entries are found.
*/
xa_for_each(&tctx->xa, index, node) {
WARN_ON_ONCE(1);
break;
}
WARN_ON_ONCE(tctx->io_wq);
WARN_ON_ONCE(tctx->cached_refs);