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git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
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Youngjun Park
c13a0316ae
Patch series "mm/swap, PM: hibernate: fix swapoff race in uswsusp by pinning swap device", v8. Currently, in the uswsusp path, only the swap type value is retrieved at lookup time without holding a reference. If swapoff races after the type is acquired, subsequent slot allocations operate on a stale swap device. Additionally, grabbing and releasing the swap device reference on every slot allocation is inefficient across the entire hibernation swap path. This patch series addresses these issues: - Patch 1: Fixes the swapoff race in uswsusp by pinning the swap device from the point it is looked up until the session completes. - Patch 2: Removes the overhead of per-slot reference counting in alloc/free paths and cleans up the redundant SWP_WRITEOK check. This patch (of 2): Hibernation via uswsusp (/dev/snapshot ioctls) has a race window: after selecting the resume swap area but before user space is frozen, swapoff may run and invalidate the selected swap device. Fix this by pinning the swap device with SWP_HIBERNATION while it is in use. The pin is exclusive, which is sufficient since hibernate_acquire() already prevents concurrent hibernation sessions. The kernel swsusp path (sysfs-based hibernate/resume) uses find_hibernation_swap_type() which is not affected by the pin. It freezes user space before touching swap, so swapoff cannot race. Introduce dedicated helpers: - pin_hibernation_swap_type(): Look up and pin the swap device. Used by the uswsusp path. - find_hibernation_swap_type(): Lookup without pinning. Used by the kernel swsusp path. - unpin_hibernation_swap_type(): Clear the hibernation pin. While a swap device is pinned, swapoff is prevented from proceeding. Link: https://lore.kernel.org/[email protected] Link: https://lore.kernel.org/[email protected] Signed-off-by: Youngjun Park <[email protected]> Reviewed-by: Kairui Song <[email protected]> Cc: Baoquan He <[email protected]> Cc: Barry Song <[email protected]> Cc: Chris Li <[email protected]> Cc: Kemeng Shi <[email protected]> Cc: Nhat Pham <[email protected]> Cc: "Rafael J . Wysocki" <[email protected]> Signed-off-by: Andrew Morton <[email protected]>