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staging: zcache: fix cleancache race condition with shrinker
This patch fixes a race condition that results in memory corruption when using cleancache. The race exists between the zcache shrinker handler, shrink_zcache_memory() and cleancache_get_page(). In most cases, the shrinker will both evict a zbpg from its buddy list and flush it from tmem before a cleancache_get_page() occurs on that page. A subsequent cleancache_get_page() will fail in the tmem layer. In the rare case that two occur together and the cleancache_get_page() path gets through the tmem layer before the shrinker path can flush tmem, zbud_decompress() does a check to see if the zbpg is a "zombie", i.e. not on a buddy list, which means the shrinker is in the process of reclaiming it. If the zbpg is a zombie, zbud_decompress() returns -EINVAL. However, this return code is being ignored by the caller, zcache_pampd_get_data_and_free(), which results in the caller of cleancache_get_page() thinking that the page has been properly retrieved when it has not. This patch modifies zcache_pampd_get_data_and_free() to convey the failure up the stack so that the caller of cleancache_get_page() knows the page retrieval failed. This needs to be applied to stable trees as well. zcache-main.c was named zcache.c before v3.1, so I'm not sure how you want to handle trees earlier than that. Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: stable <stable@vger.kernel.org> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 3 additions and 4 deletions
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@ -1251,13 +1251,12 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *bufsize, bool raw,
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void *pampd, struct tmem_pool *pool,
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struct tmem_oid *oid, uint32_t index)
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{
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int ret = 0;
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BUG_ON(!is_ephemeral(pool));
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zbud_decompress((struct page *)(data), pampd);
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if (zbud_decompress((struct page *)(data), pampd) < 0)
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return -EINVAL;
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zbud_free_and_delist((struct zbud_hdr *)pampd);
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atomic_dec(&zcache_curr_eph_pampd_count);
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return ret;
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return 0;
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}
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/*
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