| Message ID | 20250208184928.219960-1-richard120310@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: pgtable: Ensure pml spinlock gets unlock | expand |
On 2025/2/9 02:49, I Hsin Cheng wrote: > When !start_pte is true, the "pml" spinlock is still being holded and > the branch "out_pte" is taken. If "ptl" is equal to "pml", the lock > "pml" will still be locked when the function returns. No. When start_pte is NULL, the ptl must also be NULL, so the ptl and pml will not be equal. > > It'll be better to set a new branch "out_pte" and jump to it when > !start_pte is true at the first place, therefore no additional check for > "start_pte" or "ptl != pml" is needed, simply unlock "pml" and return. > > Signed-off-by: I Hsin Cheng <richard120310@gmail.com> > --- > mm/pt_reclaim.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c > index 7e9455a18aae..163e38f1728d 100644 > --- a/mm/pt_reclaim.c > +++ b/mm/pt_reclaim.c > @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, > pml = pmd_lock(mm, pmd); > start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl); > if (!start_pte) > - goto out_ptl; > + goto out_pte; > if (ptl != pml) > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > > @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, > pte_unmap_unlock(start_pte, ptl); > if (ptl != pml) > spin_unlock(pml); > + return; > + > +out_pte: > + spin_unlock(pml); > }
On Mon, Feb 10, 2025 at 12:05:05PM +0800, Qi Zheng wrote: > > > On 2025/2/9 02:49, I Hsin Cheng wrote: > > When !start_pte is true, the "pml" spinlock is still being holded and > > the branch "out_pte" is taken. If "ptl" is equal to "pml", the lock > > "pml" will still be locked when the function returns. > > No. When start_pte is NULL, the ptl must also be NULL, so the ptl and > pml will not be equal. > > > > > It'll be better to set a new branch "out_pte" and jump to it when > > !start_pte is true at the first place, therefore no additional check for > > "start_pte" or "ptl != pml" is needed, simply unlock "pml" and return. > > > > Signed-off-by: I Hsin Cheng <richard120310@gmail.com> > > --- > > mm/pt_reclaim.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c > > index 7e9455a18aae..163e38f1728d 100644 > > --- a/mm/pt_reclaim.c > > +++ b/mm/pt_reclaim.c > > @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, > > pml = pmd_lock(mm, pmd); > > start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl); > > if (!start_pte) > > - goto out_ptl; > > + goto out_pte; > > if (ptl != pml) > > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > > @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, > > pte_unmap_unlock(start_pte, ptl); > > if (ptl != pml) > > spin_unlock(pml); > > + return; > > + > > +out_pte: > > + spin_unlock(pml); > > } Hi Qi, Thanks for your kindly review! > No. When start_pte is NULL, the ptl must also be NULL, so the ptl and > pml will not be equal. Since this is the case, we don't have to do any addtional check for "start_pte" and "ptl != pml", we can be sure that only the second check will be true so we can unlock "pml" without the redundant check, that's my understanding, what do you think? Best regards, I Hsin Cheng
On 2025/2/10 16:20, I Hsin Cheng wrote: > On Mon, Feb 10, 2025 at 12:05:05PM +0800, Qi Zheng wrote: >> >> >> On 2025/2/9 02:49, I Hsin Cheng wrote: >>> When !start_pte is true, the "pml" spinlock is still being holded and >>> the branch "out_pte" is taken. If "ptl" is equal to "pml", the lock >>> "pml" will still be locked when the function returns. >> >> No. When start_pte is NULL, the ptl must also be NULL, so the ptl and >> pml will not be equal. >> >>> >>> It'll be better to set a new branch "out_pte" and jump to it when >>> !start_pte is true at the first place, therefore no additional check for >>> "start_pte" or "ptl != pml" is needed, simply unlock "pml" and return. >>> >>> Signed-off-by: I Hsin Cheng <richard120310@gmail.com> >>> --- >>> mm/pt_reclaim.c | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c >>> index 7e9455a18aae..163e38f1728d 100644 >>> --- a/mm/pt_reclaim.c >>> +++ b/mm/pt_reclaim.c >>> @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, >>> pml = pmd_lock(mm, pmd); >>> start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl); >>> if (!start_pte) >>> - goto out_ptl; >>> + goto out_pte; >>> if (ptl != pml) >>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); >>> @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, >>> pte_unmap_unlock(start_pte, ptl); >>> if (ptl != pml) >>> spin_unlock(pml); >>> + return; >>> + >>> +out_pte: >>> + spin_unlock(pml); >>> } > > Hi Qi, > > Thanks for your kindly review! > >> No. When start_pte is NULL, the ptl must also be NULL, so the ptl and >> pml will not be equal. > > Since this is the case, we don't have to do any addtional check for > "start_pte" and "ptl != pml", we can be sure that only the second check > will be true so we can unlock "pml" without the redundant check, that's > my understanding, what do you think? Adding a label vs Redundant check in rare cases Not sure if this is worth it. ;) > > Best regards, > I Hsin Cheng > >
On 2025/2/10 16:31, Qi Zheng wrote: > [...] >>>> >>>> diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c >>>> index 7e9455a18aae..163e38f1728d 100644 >>>> --- a/mm/pt_reclaim.c >>>> +++ b/mm/pt_reclaim.c >>>> @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t >>>> *pmd, unsigned long addr, >>>> pml = pmd_lock(mm, pmd); >>>> start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, >>>> &ptl); >>>> if (!start_pte) Maybe we can return directly here: if (!start_pte) { spin_unlock(pml); return; } >>>> - goto out_ptl; >>>> + goto out_pte; >>>> if (ptl != pml) >>>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); >>>> @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t >>>> *pmd, unsigned long addr, >>>> pte_unmap_unlock(start_pte, ptl); >>>> if (ptl != pml) >>>> spin_unlock(pml); >>>> + return; >>>> + >>>> +out_pte: >>>> + spin_unlock(pml); >>>> } >>
On Mon, Feb 10, 2025 at 04:42:13PM +0800, Qi Zheng wrote: > > > On 2025/2/10 16:31, Qi Zheng wrote: > > > > [...] > > > > > > > > > > > diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c > > > > > index 7e9455a18aae..163e38f1728d 100644 > > > > > --- a/mm/pt_reclaim.c > > > > > +++ b/mm/pt_reclaim.c > > > > > @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, > > > > > pmd_t *pmd, unsigned long addr, > > > > > pml = pmd_lock(mm, pmd); > > > > > start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, > > > > > &pmdval, &ptl); > > > > > if (!start_pte) > > Maybe we can return directly here: > > if (!start_pte) { > spin_unlock(pml); > return; > } > > > > > > - goto out_ptl; > > > > > + goto out_pte; > > > > > if (ptl != pml) > > > > > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > > > > > @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, > > > > > pmd_t *pmd, unsigned long addr, > > > > > pte_unmap_unlock(start_pte, ptl); > > > > > if (ptl != pml) > > > > > spin_unlock(pml); > > > > > + return; > > > > > + > > > > > +out_pte: > > > > > + spin_unlock(pml); > > > > > } > > > Hi Qi, > Maybe we can return directly here: > > if (!start_pte) { > spin_unlock(pml); > return; > } Ahh that's right I think it's better than adding another label, it doesn't even need to jump. Should I send patch v2 for it or wait for the maintainer's review first? Best regards, I Hsin Cheng
On Mon, Feb 10, 2025 at 04:42:13PM +0800, Qi Zheng wrote: > > > On 2025/2/10 16:31, Qi Zheng wrote: > > > > [...] > > > > > > > > > > > diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c > > > > > index 7e9455a18aae..163e38f1728d 100644 > > > > > --- a/mm/pt_reclaim.c > > > > > +++ b/mm/pt_reclaim.c > > > > > @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, > > > > > pmd_t *pmd, unsigned long addr, > > > > > pml = pmd_lock(mm, pmd); > > > > > start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, > > > > > &pmdval, &ptl); > > > > > if (!start_pte) > > Maybe we can return directly here: > > if (!start_pte) { > spin_unlock(pml); > return; > } > > > > > > - goto out_ptl; > > > > > + goto out_pte; > > > > > if (ptl != pml) > > > > > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > > > > > @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, > > > > > pmd_t *pmd, unsigned long addr, > > > > > pte_unmap_unlock(start_pte, ptl); > > > > > if (ptl != pml) > > > > > spin_unlock(pml); > > > > > + return; > > > > > + > > > > > +out_pte: > > > > > + spin_unlock(pml); > > > > > } > > > I've send a new patch stating for this change and change the title, because pml will sure get unlocked, we just prevent the redundant branches. Best regards, I Hsin Cheng
diff --git a/mm/pt_reclaim.c b/mm/pt_reclaim.c index 7e9455a18aae..163e38f1728d 100644 --- a/mm/pt_reclaim.c +++ b/mm/pt_reclaim.c @@ -43,7 +43,7 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, pml = pmd_lock(mm, pmd); start_pte = pte_offset_map_rw_nolock(mm, pmd, addr, &pmdval, &ptl); if (!start_pte) - goto out_ptl; + goto out_pte; if (ptl != pml) spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); @@ -68,4 +68,8 @@ void try_to_free_pte(struct mm_struct *mm, pmd_t *pmd, unsigned long addr, pte_unmap_unlock(start_pte, ptl); if (ptl != pml) spin_unlock(pml); + return; + +out_pte: + spin_unlock(pml); }
When !start_pte is true, the "pml" spinlock is still being holded and the branch "out_pte" is taken. If "ptl" is equal to "pml", the lock "pml" will still be locked when the function returns. It'll be better to set a new branch "out_pte" and jump to it when !start_pte is true at the first place, therefore no additional check for "start_pte" or "ptl != pml" is needed, simply unlock "pml" and return. Signed-off-by: I Hsin Cheng <richard120310@gmail.com> --- mm/pt_reclaim.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)