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

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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>
This commit is contained in:
Jens Axboe 2024-11-29 07:20:28 -07:00
parent 43eef70e7e
commit 7eb75ce752
1 changed files with 12 additions and 1 deletions
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13
io_uring/tctx.c
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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);