The NFS client writeback paths change which flags are passed to their
memory allocation calls based on whether the current task is running from
within a workqueue or not. More specifically, it appears that during
writeback allocations with PF_WQ_WORKER set on current->flags will add
__GFP_NORETRY | __GFP_NOWARN. Presumably this is because nfsiod can
simply fail quickly and later retry to write back that specific page should
the allocation fail.
However, the check for PF_WQ_WORKER is too general because tasks can enter NFS
writeback paths from other workqueues. Specifically, the loopback driver
tends to perform writeback into backing files on NFS with PF_WQ_WORKER set,
and additionally sets PF_MEMALLOC_NOIO. The combination of
PF_MEMALLOC_NOIO with __GFP_NORETRY can easily result in allocation
failures and the loopback driver has no retry functionality. As a result,
after commit 0bae835b63c5 ("NFS: Avoid writeback threads getting stuck in
mempool_alloc()") users are seeing corrupted loop-mounted filesystems backed
by image files on NFS.
In a preceding patch, we introduced a function to allow NFS to detect if
the task is executing within a specific workqueue. Here we use that helper
to set __GFP_NORETRY | __GFP_NOWARN only if the workqueue is nfsiod.
Fixes: 0bae835b63c5 ("NFS: Avoid writeback threads getting stuck in mempool_alloc()")
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
---
fs/nfs/internal.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 69c2c10ee658..173172afa3f5 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -12,6 +12,7 @@
#include <linux/nfs_page.h>
#include <linux/nfslocalio.h>
#include <linux/wait_bit.h>
+#include <linux/workqueue.h>
#define NFS_SB_MASK (SB_NOSUID|SB_NODEV|SB_NOEXEC|SB_SYNCHRONOUS)
@@ -669,9 +670,18 @@ nfs_write_match_verf(const struct nfs_writeverf *verf,
!nfs_write_verifier_cmp(&req->wb_verf, &verf->verifier);
}
+static inline bool is_nfsiod(void)
+{
+ struct workqueue_struct *current_wq = current_workqueue();
+
+ if (current_wq)
+ return current_wq == nfsiod_workqueue;
+ return false;
+}
+
static inline gfp_t nfs_io_gfp_mask(void)
{
- if (current->flags & PF_WQ_WORKER)
+ if (is_nfsiod())
return GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
return GFP_KERNEL;
}
--
2.47.0
