4.9-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 9a24ce5b66f9c8190d63b15f4473600db4935f1f ]
[Description]
In a heavily loaded system where the system pagecache is nearing memory limits and fscache is enabled, pages can be leaked by fscache while trying read pages from cachefiles backend. This can happen because two applications can be reading same page from a single mount, two threads can be trying to read the backing page at same time. This results in one of the threads finding that a page for the backing file or netfs file is already in the radix tree. During the error handling cachefiles does not clean up the reference on backing page, leading to page leak.
[Fix] The fix is straightforward, to decrement the reference when error is encountered.
[dhowells: Note that I've removed the clearance and put of newpage as they aren't attested in the commit message and don't appear to actually achieve anything since a new page is only allocated is newpage!=NULL and any residual new page is cleared before returning.]
[Testing] I have tested the fix using following method for 12+ hrs.
1) mkdir -p /mnt/nfs ; mount -o vers=3,fsc <server_ip>:/export /mnt/nfs 2) create 10000 files of 2.8MB in a NFS mount. 3) start a thread to simulate heavy VM presssure (while true ; do echo 3 > /proc/sys/vm/drop_caches ; sleep 1 ; done)& 4) start multiple parallel reader for data set at same time find /mnt/nfs -type f | xargs -P 80 cat > /dev/null & find /mnt/nfs -type f | xargs -P 80 cat > /dev/null & find /mnt/nfs -type f | xargs -P 80 cat > /dev/null & .. .. find /mnt/nfs -type f | xargs -P 80 cat > /dev/null & find /mnt/nfs -type f | xargs -P 80 cat > /dev/null & 5) finally check using cat /proc/fs/fscache/stats | grep -i pages ; free -h , cat /proc/meminfo and page-types -r -b lru to ensure all pages are freed.
Reviewed-by: Daniel Axtens dja@axtens.net Signed-off-by: Shantanu Goel sgoel01@yahoo.com Signed-off-by: Kiran Kumar Modukuri kiran.modukuri@gmail.com [dja: forward ported to current upstream] Signed-off-by: Daniel Axtens dja@axtens.net Signed-off-by: David Howells dhowells@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/cachefiles/rdwr.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c index 5e3bc9de7a16..8d43306c038b 100644 --- a/fs/cachefiles/rdwr.c +++ b/fs/cachefiles/rdwr.c @@ -537,7 +537,10 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object, netpage->index, cachefiles_gfp); if (ret < 0) { if (ret == -EEXIST) { + put_page(backpage); + backpage = NULL; put_page(netpage); + netpage = NULL; fscache_retrieval_complete(op, 1); continue; } @@ -610,7 +613,10 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object, netpage->index, cachefiles_gfp); if (ret < 0) { if (ret == -EEXIST) { + put_page(backpage); + backpage = NULL; put_page(netpage); + netpage = NULL; fscache_retrieval_complete(op, 1); continue; }