Messages in this thread | | | Subject | Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) | From | Vlastimil Babka <> | Date | Thu, 22 Sep 2016 18:56:48 +0200 |
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On 09/22/2016 06:49 PM, Eric Dumazet wrote: > On Thu, 2016-09-22 at 18:43 +0200, Vlastimil Babka wrote: >> The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows >> with the number of fds passed. We had a customer report page allocation >> failures of order-4 for this allocation. This is a costly order, so it might >> easily fail, as the VM expects such allocation to have a lower-order fallback. >> >> Such trivial fallback is vmalloc(), as the memory doesn't have to be >> physically contiguous. Also the allocation is temporary for the duration of the >> syscall, so it's unlikely to stress vmalloc too much. > > vmalloc() uses a vmap_area_lock spinlock, and TLB flushes. > > So I guess allowing vmalloc() being called from an innocent application > doing a select() might be dangerous, especially if this select() happens > thousands of time per second.
Isn't seq_buf_alloc() similarly exposed? And ipc_alloc()?
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