From: kmodukuri <[email protected]> Note: This is the version 2 of the patch containing additional fixes, following the ported change by Daniel, Axtens and original change by Shantanu, Goel.
[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 thread finding that a page for the backing file or netfs file is already in the radix tree. During the error handling cachefiles does not cleanup the reference on backing page, leading to page leak. [Fix] The fix is straightforward, to decrement the reference when error is encounterd. [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. Subject: [PATCH:v2] cachefiles: page reference leak fix when vmscan is active Signed-off-by: Shantanu Goel <[email protected]> Signed-off-by: Kiran Kumar Modukuri <[email protected]> [dja: forward ported to current upstream] Signed-off-by: Daniel Axtens <[email protected]> --- fs/cachefiles/rdwr.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c index 40f7595..9dc87d4 100644 --- a/fs/cachefiles/rdwr.c +++ b/fs/cachefiles/rdwr.c @@ -274,6 +274,8 @@ static int cachefiles_read_backing_file_one(struct cachefiles_object *object, goto installed_new_backing_page; if (ret != -EEXIST) goto nomem_page; + put_page(newpage); + newpage = NULL; } /* we've installed a new backing page, so now we need to start @@ -511,6 +513,8 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object, goto installed_new_backing_page; if (ret != -EEXIST) goto nomem; + put_page(newpage); + newpage = NULL; } /* we've installed a new backing page, so now we need @@ -535,7 +539,10 @@ 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; } @@ -608,6 +615,8 @@ 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); fscache_retrieval_complete(op, 1); continue; -- 2.7.4 -- Linux-cachefs mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-cachefs
