| Message ID | 1592637174-19657-1-git-send-email-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection | expand |
On Sat, Jun 20, 2020 at 03:12:54AM -0400, Yafang Shao wrote: > PF_FSTRANS which is used to avoid transaction reservation recursion, is > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to > PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce > memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which > means to avoid filesystem reclaim recursion. That change is subtle. > Let's take the exmple of the check of WARN_ON_ONCE(current->flags & > PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to > PF_MEMALLOC_NOFS is not proper. > > Bellow comment is quoted from Dave, > > It wasn't for memory allocation recursion protection in XFS - it was for > > transaction reservation recursion protection by something trying to flush > > data pages while holding a transaction reservation. Doing > > this could deadlock the journal because the existing reservation > > could prevent the nested reservation for being able to reserve space > > in the journal and that is a self-deadlock vector. > > IOWs, this check is not protecting against memory reclaim recursion > > bugs at all (that's the previous check [1]). This check is > > protecting against the filesystem calling writepages directly from a > > context where it can self-deadlock. > > So what we are seeing here is that the PF_FSTRANS -> > > PF_MEMALLOC_NOFS abstraction lost all the actual useful information > > about what type of error this check was protecting against. > > Besides reintroducing PF_FSTRANS, there're some other improvements in this > patch, > - Remove useless MACRO current_clear_flags_nested(), current_pid() and > current_test_flags(). > - Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc() > > [1]. Bellow check is to avoid memory reclaim recursion. > if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == > PF_MEMALLOC)) > goto redirty; > > Cc: Dave Chinner <david@fromorbit.com> > Cc: Michal Hocko <mhocko@kernel.org> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > --- > fs/iomap/buffered-io.c | 4 ++-- > fs/xfs/kmem.c | 7 ------- > fs/xfs/kmem.h | 2 +- > fs/xfs/libxfs/xfs_btree.c | 2 +- > fs/xfs/xfs_aops.c | 4 ++-- > fs/xfs/xfs_linux.h | 4 ---- > fs/xfs/xfs_trans.c | 12 ++++++------ > include/linux/sched.h | 1 + > 8 files changed, 13 insertions(+), 23 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index bcfc288..0f1945c 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio) > > /* > * Given that we do not allow direct reclaim to call us, we should > - * never be called in a recursive filesystem reclaim context. > + * never be called while in a filesystem transaction. > */ > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > + if (WARN_ON_ONCE(current->flags & PF_FSTRANS)) > goto redirty; This is OK, but the rest of the patch is not. I did not say "replace all XFS use of GFP_NOFS/KM_NOFS with PF_TRANS", which is what this patch does. The use of PF_MEMALLOC_NOFS within transactions is correct and valid and needs to remain. Replacing this with PF_FSTRANS effectively reverts all the simplifications and obviously self-documneting code that PF_MEMALLOC_NOFS provides us with. IOWs, PF_MEMALLOC_NOFS is used to indicate that this is a "no reclaim recursion" path and so it's use remains completely unchanged in XFS. PF_FSTRANS is to indicate this is a "no transaction recursion" path, which is a different thing and needs it's own specific annotation. > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c > index f136647..9875a23 100644 > --- a/fs/xfs/kmem.c > +++ b/fs/xfs/kmem.c > @@ -41,18 +41,11 @@ > static void * > __kmem_vmalloc(size_t size, xfs_km_flags_t flags) > { > - unsigned nofs_flag = 0; > void *ptr; > gfp_t lflags = kmem_flags_convert(flags); > > - if (flags & KM_NOFS) > - nofs_flag = memalloc_nofs_save(); > - > ptr = __vmalloc(size, lflags); > > - if (flags & KM_NOFS) > - memalloc_nofs_restore(nofs_flag); > - This breaks both kmem_alloc_large() and kmem_alloc_io() if they are called from an explicit KM_NOFS context. vmalloc() does not respect the gfp flags that are passed to it and will always do GFP_KERNEL allocations deep down in the page table allocation code, and hence we must use memalloc_nofs_save() here if called in a KM_NOFS context. > return ptr; > } > > diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h > index 34cbcfd..ccc63de 100644 > --- a/fs/xfs/kmem.h > +++ b/fs/xfs/kmem.h > @@ -34,7 +34,7 @@ > BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP)); > > lflags = GFP_KERNEL | __GFP_NOWARN; > - if (flags & KM_NOFS) > + if (current->flags & PF_FSTRANS || flags & KM_NOFS) > lflags &= ~__GFP_FS; No. If we are in a transaction context, PF_MEMALLOC_NOFS should be set. We got rid of all the PF_FSTRANS checks out of this code by moving to PF_MEMALLOC_NOFS, reverting this isn't an improvement. > > /* > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > index 2d25bab..65d0afe 100644 > --- a/fs/xfs/libxfs/xfs_btree.c > +++ b/fs/xfs/libxfs/xfs_btree.c > @@ -2814,7 +2814,7 @@ struct xfs_btree_split_args { > struct xfs_btree_split_args *args = container_of(work, > struct xfs_btree_split_args, work); > unsigned long pflags; > - unsigned long new_pflags = PF_MEMALLOC_NOFS; > + unsigned long new_pflags = PF_FSTRANS; new_pflags = PF_MEMALLOC_NOFS | PF_FSTRANS; > > /* > * we are in a transaction context here, but may also be doing work > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > index b356118..02733eb 100644 > --- a/fs/xfs/xfs_aops.c > +++ b/fs/xfs/xfs_aops.c > @@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) > * We hand off the transaction to the completion thread now, so > * clear the flag here. > */ > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); current_restore_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS); > return 0; > } > > @@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) > * thus we need to mark ourselves as being in a transaction manually. > * Similarly for freeze protection. > */ > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); current_set_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS); > __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS); > > /* we abort the update if there was an IO error */ > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h > index 9f70d2f..ab737fe 100644 > --- a/fs/xfs/xfs_linux.h > +++ b/fs/xfs/xfs_linux.h > @@ -102,12 +102,8 @@ > #define xfs_cowb_secs xfs_params.cowb_timer.val > > #define current_cpu() (raw_smp_processor_id()) > -#define current_pid() (current->pid) > -#define current_test_flags(f) (current->flags & (f)) > #define current_set_flags_nested(sp, f) \ > (*(sp) = current->flags, current->flags |= (f)) > -#define current_clear_flags_nested(sp, f) \ > - (*(sp) = current->flags, current->flags &= ~(f)) > #define current_restore_flags_nested(sp, f) \ > (current->flags = ((current->flags & ~(f)) | (*(sp) & (f)))) Separate cleanup patch to remove unrelated definitions, please. > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > index 3c94e5f..1c1b982 100644 > --- a/fs/xfs/xfs_trans.c > +++ b/fs/xfs/xfs_trans.c > @@ -153,7 +153,7 @@ > bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0; > > /* Mark this thread as being in a transaction */ > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); > And, again, PF_FSTRANS | PF_MEMALLOC_NOFS through this code. Cheers, Dave.
On Mon, Jun 22, 2020 at 7:04 AM Dave Chinner <david@fromorbit.com> wrote: > > On Sat, Jun 20, 2020 at 03:12:54AM -0400, Yafang Shao wrote: > > PF_FSTRANS which is used to avoid transaction reservation recursion, is > > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to > > PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce > > memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which > > means to avoid filesystem reclaim recursion. That change is subtle. > > Let's take the exmple of the check of WARN_ON_ONCE(current->flags & > > PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to > > PF_MEMALLOC_NOFS is not proper. > > > > Bellow comment is quoted from Dave, > > > It wasn't for memory allocation recursion protection in XFS - it was for > > > transaction reservation recursion protection by something trying to flush > > > data pages while holding a transaction reservation. Doing > > > this could deadlock the journal because the existing reservation > > > could prevent the nested reservation for being able to reserve space > > > in the journal and that is a self-deadlock vector. > > > IOWs, this check is not protecting against memory reclaim recursion > > > bugs at all (that's the previous check [1]). This check is > > > protecting against the filesystem calling writepages directly from a > > > context where it can self-deadlock. > > > So what we are seeing here is that the PF_FSTRANS -> > > > PF_MEMALLOC_NOFS abstraction lost all the actual useful information > > > about what type of error this check was protecting against. > > > > Besides reintroducing PF_FSTRANS, there're some other improvements in this > > patch, > > - Remove useless MACRO current_clear_flags_nested(), current_pid() and > > current_test_flags(). > > - Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc() > > > > [1]. Bellow check is to avoid memory reclaim recursion. > > if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == > > PF_MEMALLOC)) > > goto redirty; > > > > Cc: Dave Chinner <david@fromorbit.com> > > Cc: Michal Hocko <mhocko@kernel.org> > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > > --- > > fs/iomap/buffered-io.c | 4 ++-- > > fs/xfs/kmem.c | 7 ------- > > fs/xfs/kmem.h | 2 +- > > fs/xfs/libxfs/xfs_btree.c | 2 +- > > fs/xfs/xfs_aops.c | 4 ++-- > > fs/xfs/xfs_linux.h | 4 ---- > > fs/xfs/xfs_trans.c | 12 ++++++------ > > include/linux/sched.h | 1 + > > 8 files changed, 13 insertions(+), 23 deletions(-) > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > index bcfc288..0f1945c 100644 > > --- a/fs/iomap/buffered-io.c > > +++ b/fs/iomap/buffered-io.c > > @@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio) > > > > /* > > * Given that we do not allow direct reclaim to call us, we should > > - * never be called in a recursive filesystem reclaim context. > > + * never be called while in a filesystem transaction. > > */ > > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > > + if (WARN_ON_ONCE(current->flags & PF_FSTRANS)) > > goto redirty; > > This is OK, but the rest of the patch is not. > > I did not say "replace all XFS use of GFP_NOFS/KM_NOFS with > PF_TRANS", which is what this patch does. The use of > PF_MEMALLOC_NOFS within transactions is correct and valid and needs > to remain. Replacing this with PF_FSTRANS effectively reverts all > the simplifications and obviously self-documneting code that > PF_MEMALLOC_NOFS provides us with. > Sorry about that, I misunderstood it. Will correct it in the next version. > IOWs, PF_MEMALLOC_NOFS is used to indicate that this is a "no > reclaim recursion" path and so it's use remains completely unchanged > in XFS. PF_FSTRANS is to indicate this is a "no > transaction recursion" path, which is a different thing and needs > it's own specific annotation. > Thanks for the explanation. > > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c > > index f136647..9875a23 100644 > > --- a/fs/xfs/kmem.c > > +++ b/fs/xfs/kmem.c > > @@ -41,18 +41,11 @@ > > static void * > > __kmem_vmalloc(size_t size, xfs_km_flags_t flags) > > { > > - unsigned nofs_flag = 0; > > void *ptr; > > gfp_t lflags = kmem_flags_convert(flags); > > > > - if (flags & KM_NOFS) > > - nofs_flag = memalloc_nofs_save(); > > - > > ptr = __vmalloc(size, lflags); > > > > - if (flags & KM_NOFS) > > - memalloc_nofs_restore(nofs_flag); > > - > > This breaks both kmem_alloc_large() and kmem_alloc_io() if they are > called from an explicit KM_NOFS context. vmalloc() does not respect > the gfp flags that are passed to it and will always do GFP_KERNEL > allocations deep down in the page table allocation code, and hence > we must use memalloc_nofs_save() here if called in a KM_NOFS > context. > I thought kmem_flags_convert() has already checked KM_NOFS so we don't need to call memalloc_nofs_save(), but it seems I was wrong. Thanks for the clarification. > > return ptr; > > } > > > > diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h > > index 34cbcfd..ccc63de 100644 > > --- a/fs/xfs/kmem.h > > +++ b/fs/xfs/kmem.h > > @@ -34,7 +34,7 @@ > > BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP)); > > > > lflags = GFP_KERNEL | __GFP_NOWARN; > > - if (flags & KM_NOFS) > > + if (current->flags & PF_FSTRANS || flags & KM_NOFS) > > lflags &= ~__GFP_FS; > > No. If we are in a transaction context, PF_MEMALLOC_NOFS should be > set. We got rid of all the PF_FSTRANS checks out of this code by > moving to PF_MEMALLOC_NOFS, reverting this isn't an improvement. > Got it. Thanks. > > > > /* > > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > > index 2d25bab..65d0afe 100644 > > --- a/fs/xfs/libxfs/xfs_btree.c > > +++ b/fs/xfs/libxfs/xfs_btree.c > > @@ -2814,7 +2814,7 @@ struct xfs_btree_split_args { > > struct xfs_btree_split_args *args = container_of(work, > > struct xfs_btree_split_args, work); > > unsigned long pflags; > > - unsigned long new_pflags = PF_MEMALLOC_NOFS; > > + unsigned long new_pflags = PF_FSTRANS; > > new_pflags = PF_MEMALLOC_NOFS | PF_FSTRANS; > > > > /* > > * we are in a transaction context here, but may also be doing work > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > index b356118..02733eb 100644 > > --- a/fs/xfs/xfs_aops.c > > +++ b/fs/xfs/xfs_aops.c > > @@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) > > * We hand off the transaction to the completion thread now, so > > * clear the flag here. > > */ > > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > > + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); > > current_restore_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS); > Thanks > > return 0; > > } > > > > @@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) > > * thus we need to mark ourselves as being in a transaction manually. > > * Similarly for freeze protection. > > */ > > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); > > current_set_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS); > Thanks > > __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS); > > > > /* we abort the update if there was an IO error */ > > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h > > index 9f70d2f..ab737fe 100644 > > --- a/fs/xfs/xfs_linux.h > > +++ b/fs/xfs/xfs_linux.h > > @@ -102,12 +102,8 @@ > > #define xfs_cowb_secs xfs_params.cowb_timer.val > > > > #define current_cpu() (raw_smp_processor_id()) > > -#define current_pid() (current->pid) > > -#define current_test_flags(f) (current->flags & (f)) > > #define current_set_flags_nested(sp, f) \ > > (*(sp) = current->flags, current->flags |= (f)) > > -#define current_clear_flags_nested(sp, f) \ > > - (*(sp) = current->flags, current->flags &= ~(f)) > > #define current_restore_flags_nested(sp, f) \ > > (current->flags = ((current->flags & ~(f)) | (*(sp) & (f)))) > > Separate cleanup patch to remove unrelated definitions, please. > Sure, I will. > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > index 3c94e5f..1c1b982 100644 > > --- a/fs/xfs/xfs_trans.c > > +++ b/fs/xfs/xfs_trans.c > > @@ -153,7 +153,7 @@ > > bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0; > > > > /* Mark this thread as being in a transaction */ > > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); > > > > And, again, PF_FSTRANS | PF_MEMALLOC_NOFS through this code. > Thanks
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index bcfc288..0f1945c 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio) /* * Given that we do not allow direct reclaim to call us, we should - * never be called in a recursive filesystem reclaim context. + * never be called while in a filesystem transaction. */ - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) + if (WARN_ON_ONCE(current->flags & PF_FSTRANS)) goto redirty; /* diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c index f136647..9875a23 100644 --- a/fs/xfs/kmem.c +++ b/fs/xfs/kmem.c @@ -41,18 +41,11 @@ static void * __kmem_vmalloc(size_t size, xfs_km_flags_t flags) { - unsigned nofs_flag = 0; void *ptr; gfp_t lflags = kmem_flags_convert(flags); - if (flags & KM_NOFS) - nofs_flag = memalloc_nofs_save(); - ptr = __vmalloc(size, lflags); - if (flags & KM_NOFS) - memalloc_nofs_restore(nofs_flag); - return ptr; } diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h index 34cbcfd..ccc63de 100644 --- a/fs/xfs/kmem.h +++ b/fs/xfs/kmem.h @@ -34,7 +34,7 @@ BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP)); lflags = GFP_KERNEL | __GFP_NOWARN; - if (flags & KM_NOFS) + if (current->flags & PF_FSTRANS || flags & KM_NOFS) lflags &= ~__GFP_FS; /* diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c index 2d25bab..65d0afe 100644 --- a/fs/xfs/libxfs/xfs_btree.c +++ b/fs/xfs/libxfs/xfs_btree.c @@ -2814,7 +2814,7 @@ struct xfs_btree_split_args { struct xfs_btree_split_args *args = container_of(work, struct xfs_btree_split_args, work); unsigned long pflags; - unsigned long new_pflags = PF_MEMALLOC_NOFS; + unsigned long new_pflags = PF_FSTRANS; /* * we are in a transaction context here, but may also be doing work diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index b356118..02733eb 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) * We hand off the transaction to the completion thread now, so * clear the flag here. */ - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); return 0; } @@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend) * thus we need to mark ourselves as being in a transaction manually. * Similarly for freeze protection. */ - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS); /* we abort the update if there was an IO error */ diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h index 9f70d2f..ab737fe 100644 --- a/fs/xfs/xfs_linux.h +++ b/fs/xfs/xfs_linux.h @@ -102,12 +102,8 @@ #define xfs_cowb_secs xfs_params.cowb_timer.val #define current_cpu() (raw_smp_processor_id()) -#define current_pid() (current->pid) -#define current_test_flags(f) (current->flags & (f)) #define current_set_flags_nested(sp, f) \ (*(sp) = current->flags, current->flags |= (f)) -#define current_clear_flags_nested(sp, f) \ - (*(sp) = current->flags, current->flags &= ~(f)) #define current_restore_flags_nested(sp, f) \ (current->flags = ((current->flags & ~(f)) | (*(sp) & (f)))) diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c index 3c94e5f..1c1b982 100644 --- a/fs/xfs/xfs_trans.c +++ b/fs/xfs/xfs_trans.c @@ -153,7 +153,7 @@ bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0; /* Mark this thread as being in a transaction */ - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS); /* * Attempt to reserve the needed disk blocks by decrementing @@ -163,7 +163,7 @@ if (blocks > 0) { error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd); if (error != 0) { - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); return -ENOSPC; } tp->t_blk_res += blocks; @@ -240,7 +240,7 @@ tp->t_blk_res = 0; } - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); return error; } @@ -861,7 +861,7 @@ xfs_log_commit_cil(mp, tp, &commit_lsn, regrant); - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); xfs_trans_free(tp); /* @@ -893,7 +893,7 @@ xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket); tp->t_ticket = NULL; } - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); xfs_trans_free_items(tp, !!error); xfs_trans_free(tp); @@ -954,7 +954,7 @@ } /* mark this thread as no longer being in a transaction */ - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS); xfs_trans_free_items(tp, dirty); xfs_trans_free(tp); diff --git a/include/linux/sched.h b/include/linux/sched.h index b62e6aa..02045e8 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1511,6 +1511,7 @@ static inline int is_global_init(struct task_struct *tsk) #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ #define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */ +#define PF_FSTRANS 0x01000000 /* Inside a filesystem transaction */ #define PF_UMH 0x02000000 /* I'm an Usermodehelper process */ #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */ #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
PF_FSTRANS which is used to avoid transaction reservation recursion, is dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which means to avoid filesystem reclaim recursion. That change is subtle. Let's take the exmple of the check of WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to PF_MEMALLOC_NOFS is not proper. Bellow comment is quoted from Dave, > It wasn't for memory allocation recursion protection in XFS - it was for > transaction reservation recursion protection by something trying to flush > data pages while holding a transaction reservation. Doing > this could deadlock the journal because the existing reservation > could prevent the nested reservation for being able to reserve space > in the journal and that is a self-deadlock vector. > IOWs, this check is not protecting against memory reclaim recursion > bugs at all (that's the previous check [1]). This check is > protecting against the filesystem calling writepages directly from a > context where it can self-deadlock. > So what we are seeing here is that the PF_FSTRANS -> > PF_MEMALLOC_NOFS abstraction lost all the actual useful information > about what type of error this check was protecting against. Besides reintroducing PF_FSTRANS, there're some other improvements in this patch, - Remove useless MACRO current_clear_flags_nested(), current_pid() and current_test_flags(). - Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc() [1]. Bellow check is to avoid memory reclaim recursion. if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)) goto redirty; Cc: Dave Chinner <david@fromorbit.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Yafang Shao <laoar.shao@gmail.com> --- fs/iomap/buffered-io.c | 4 ++-- fs/xfs/kmem.c | 7 ------- fs/xfs/kmem.h | 2 +- fs/xfs/libxfs/xfs_btree.c | 2 +- fs/xfs/xfs_aops.c | 4 ++-- fs/xfs/xfs_linux.h | 4 ---- fs/xfs/xfs_trans.c | 12 ++++++------ include/linux/sched.h | 1 + 8 files changed, 13 insertions(+), 23 deletions(-)