f8e5578dca
[ Upstream commit d8c19014bba8f565d8a2f1f46b4e38d1d97bf1a7 ] The ethernet driver may allocate skb (and skb->data) via napi_alloc_skb(). This ends up to page_frag_alloc() to allocate skb->data from page_frag_cache->va. During the memory pressure, page_frag_cache->va may be allocated as pfmemalloc page. As a result, the skb->pfmemalloc is always true as skb->data is from page_frag_cache->va. The skb will be dropped if the sock (receiver) does not have SOCK_MEMALLOC. This is expected behaviour under memory pressure. However, once kernel is not under memory pressure any longer (suppose large amount of memory pages are just reclaimed), the page_frag_alloc() may still re-use the prior pfmemalloc page_frag_cache->va to allocate skb->data. As a result, the skb->pfmemalloc is always true unless page_frag_cache->va is re-allocated, even if the kernel is not under memory pressure any longer. Here is how kernel runs into issue. 1. The kernel is under memory pressure and allocation of PAGE_FRAG_CACHE_MAX_ORDER in __page_frag_cache_refill() will fail. Instead, the pfmemalloc page is allocated for page_frag_cache->va. 2: All skb->data from page_frag_cache->va (pfmemalloc) will have skb->pfmemalloc=true. The skb will always be dropped by sock without SOCK_MEMALLOC. This is an expected behaviour. 3. Suppose a large amount of pages are reclaimed and kernel is not under memory pressure any longer. We expect skb->pfmemalloc drop will not happen. 4. Unfortunately, page_frag_alloc() does not proactively re-allocate page_frag_alloc->va and will always re-use the prior pfmemalloc page. The skb->pfmemalloc is always true even kernel is not under memory pressure any longer. Fix this by freeing and re-allocating the page instead of recycling it. References: https://lore.kernel.org/lkml/20201103193239.1807-1-dongli.zhang@oracle.com/ References: https://lore.kernel.org/linux-mm/20201105042140.5253-1-willy@infradead.org/ Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com> Cc: Bert Barbe <bert.barbe@oracle.com> Cc: Rama Nichanamatlu <rama.nichanamatlu@oracle.com> Cc: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com> Cc: Manjunath Patil <manjunath.b.patil@oracle.com> Cc: Joe Jin <joe.jin@oracle.com> Cc: SRINIVAS <srinivas.eeda@oracle.com> Fixes: 79930f5892e1 ("net: do not deplete pfmemalloc reserve") Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20201115201029.11903-1-dongli.zhang@oracle.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.