CVE-2026-98079

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In the Linux kernel, the following vulnerability has been resolved: btrfs: zstd: fix lost wakeup when waiting for a workspace A writer can sleep forever in zstd_get_workspace() even though a workspace is free. When zstd_alloc_workspace() fails, the task is queued on zwsm->wait and schedules unconditionally, never re-testing the pool. zstd_put_workspace() publishes the workspace and then calls cond_wake_up(), which only wakes when a sleeper is already visible, so a workspace returned between the failed allocation and prepare_to_wait() wakes nobody. The window is wide: zstd_alloc_workspace() goes through kvmalloc() and may enter reclaim. Only a max level workspace triggers the wakeup and one is deliberately kept allocated as the fallback every waiter waits for, so once its wakeup is lost the writer stays in TASK_UNINTERRUPTIBLE until some other task happens to return one. Re-check the pool after prepare_to_wait() has published the waiter, and use the workspace if one turned up.

• git.kernel.orghttps://git.kernel.org/stable/c/0de9f31d447ae71ab08c7850a321682f8d2907c3
• git.kernel.orghttps://git.kernel.org/stable/c/2acb9f3d1cc8f65dc81ed55e238cbf8e5b60bff7
• git.kernel.orghttps://git.kernel.org/stable/c/d8f57049521948df5f50797141472fbbed3b0723

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